This is an idea that I have been fiddling around with:

In games like Pokemon and Animal Crossing, the developers utilize a real-time clock and have certain events trigger based on time and days elapsed. What I'm curious about is what kind of applications there are to making an adventure game not unlike Fable or Fallout that uses a real-time clock to contain certain events and triggers.

My initial first ideas involved fighting vampires and werewolves at night, a real night-time not a in-game night time. The other idea was given a quest that must be complete within a number of real days or even by a certain time limit so that players cannot go off and grind or do other sidequests until they feel like completing a quest.

I can definitely see downsides to using this kind of system, especially since I grew up with Animal Crossing demanding time sensitive things during school, but the game would have to be built around this system.

Other ideas I was thinking of was offering some kind of system where the character would do some kind of task while the player wasn't playing such as crafting or training so that when the player turns the game back on there is a something that wasn't there....like Fable II now that I think about it.

I don't know, does something like this seem feasible?

Well I think it would definitely limit the appeal, since many people are busy and can't play at certain times of day.

This is an idea that I have been fiddling around with:

In games like Pokemon and Animal Crossing, the developers utilize a real-time clock and have certain events trigger based on time and days elapsed. What I'm curious about is what kind of applications there are to making an adventure game not unlike Fable or Fallout that uses a real-time clock to contain certain events and triggers.

My initial first ideas involved fighting vampires and werewolves at night, a real night-time not a in-game night time. The other idea was given a quest that must be complete within a number of real days or even by a certain time limit so that players cannot go off and grind or do other sidequests until they feel like completing a quest.

I can definitely see downsides to using this kind of system, especially since I grew up with Animal Crossing demanding time sensitive things during school, but the game would have to be built around this system.

Other ideas I was thinking of was offering some kind of system where the character would do some kind of task while the player wasn't playing such as crafting or training so that when the player turns the game back on there is a something that wasn't there....like Fable II now that I think about it.

I don't know, does something like this seem feasible?

I'm not sure about this.But maybe you can try something like this.
In morning the player faces monsters but at night it gets creepy and its very dark.Maybe it can be something that is based on how soldiers fight in war, hiding at one point, finding shelter at late night unnoticed.

In my opinion, realism shouldn't get in the way of gameplay too much. Eventually it just becomes annoying, not 'immersing' or whatever you're trying to obtain with a clock system.

What would it really accomplish besides butting people out of certain events because they are working or at school during certain times of the day? It's not like you pay attention to the window when you're playing a game, anyway - sometimes I don't notice it has gotten dark during my playtime and don't really care (unless I'd planned on going out). Why should I?

There was a star-wars game, where some of the missions changed depending on the real-world time, and some things could only be unlocked at certain times.
Anyone who wanted those unlockables would just change their system clock before starting the game...

It was pretty annoying, because most people can only play games at certain times of day, or only want to play games at a certain time of day. Having the game dictate to you that you're not allowed to see some content because it doesn't like your real-life schedule is a pretty bad design choice IMO - especially for a single-player / non MMO game.

"Oh you're employed? Well I'm going to make my game less fun for you to play!"
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Non-real-time clock mechanics can be cool though. Your vampire/werewolf examples were used in Morrowind for example.

I do like some real-time clocks though, when they're not tied to the current real-world time. In the original OperationFlashpoint, a real-time clock was used (1minute in-game took 1minute), but the starting time was dictated by the mission. E.g. a particular mission would always start 2 hours before sun-set, and if you took longer than 2 hours to beat it, then you'd lose a lot of visibility. If you somehow took 10 hours to beat the mission, the sun would rise again

Utilizing the real world time in a game IS a badly designed gimmick
Utilizing fluid game time in an adventure is the most awesome thing ever

I'n morrowind/oblivion the game clock proceeded at a slightly faster rate than the real world. I think that's close to the best solution you'd get for something like this that's still fun. Or it could be matched (in time progression) with the real world, but the clock wouldn't run while you're not playing. Matching that system up with a way for players to sleep (i.e. jump forward in time) in-game so they can skip to when the next event should be.

Huh...I never really thought of it that way. I still appreciate how in some games the real-world time affects the game, but as a central mechanic, I suppose it does limit access to many people. Thanks for the input guys.

Edit:

Now lets say that this was a game being designed for a hardcore or niche crowd, so we can ignore critical appeal, how could a game like this be made without seeming too gimmicky.

I think the whole reason for even including shifting time is to help build a level of immersion. For a lot of games though, they don't use the mechanic all too well. One thing I personally found annoying in games that use a real time clock and their own in-world clock is things like shops closing when shops are important. Really nighttime is just a game's way of telling you that its time to stop and go to bed, a hiccup in most people's gameplay.

I think of a game needed to be built around using the real-world clock, it would have to use interesting elements from games that utilize the clock only a little. For example, a cool thing in Animal Crossing is that changing of the seasons and a dynamic-ish ecosystem. The new Pokemon game does that too, and while its still Autumn in the game, it looks cool. Perhaps a game like this can use a broader scale and change according to season and month.

Thinking about it now, I think using a broader system of assigning quest limits and such would work out a lot better than assigning time specific in terms of accessibility. If say a village is going to be attacked by a band of raiders, it would better to have it set at a certain day instead of a specific time and then perhaps trigger when the player is playing.

Star Wars Rogue Squadron II also had a cool mission where, depending on if it was day or night according to the internal clock, you flew a bomber or a speeder. The mission was relatively the same but how it played was quite different (a big direct attack during the day or a stealth mission at night). I think a game using a real-world clock could really benefit from making quests that can be played anytime, but perhaps only differ based on the time. For example, say a quest was given to slay a pack of werewolves, it could be done during any day as a investigation type quest, where the player must gather clues to who are the werewolves and who isn't, but if played at night it could be a strict brawler where the player takes sword and shield and fights them directly.

Of course, there would have to be a benefit to playing at actual night instead of just using an in-game clock but I think some of it will just have to rely on immersion for the players that want it. Anyone can change the internal clock to access content that they couldn't normally or didn't want to wait for, and I think that's a legitimate option for those who want something immediately instead of getting into the game world, but at least there is an option for those who would want to play in a more real-feeling world.

What if the game were easily playable in bite-sized chunks (say 5-10 minutes at a time) and played out of a browser or on a portable device?

It would make it much more feasible for a player to access content at the various times, with less constriction from their schedule, and would limit the necessity to manipulate the clock to get all the content (which defeats the purpose of the feature in the first place).

As others have said, denying people content based on the time of day they play will just be annoying. I do think that making the missions vary based on the time of day could be quite cool, as could adding real world timed elements that are activated by the player and then involve a real world time span. This could be a good way to get people coming back to your game regularly if it was a browser or mobile/handheld game like classeye suggested. I believe Farmville does something similar by having the player plant crops and then harvest them after some real world time has elapsed.

The real trick to this would be making sure that there are enough options with different time spans to suit the player's schedule. You'd want some missions where you have to wait a week or so after accepting it for the enemy general to arrive. Some that would take a few days for the next supply train to get in. Maybe one where you have to rob the bank for the secret documents but they are being moved tomorrow and are too well guarded today so that you have to wait until tonight. A group of missions that you can go off and do right now. The point is they would all need to be available at once and the player would have to be able to pick the one(s) that they want to activate for when they think they will have time to play it.

Whether or not you feel comfortable manipulating the player like this is another question, personally I have no problem with it, but I think some people do.