I am working on a concept for now of a PvP game which would be limited to phones and possibly tablets. The game will pair two people for a real-time game. I am not sure if the game is similar to anything in particular, i'm modeling it after two styles - tower defense and card games.

My question is how long should the game take - my gut feeling is it shouldn't be over 5 minutes, perhaps 4 minutes on average?. This would include all rounds, though I am trying to not have rounds. Game won't be fixed to that amount of time, but I need to have an average time in mind to figure out how gameplay should work.

How about making each round last between 1 and 3 minutes, and then letting players play as many rounds they like? (i am assuming that by "round" you didn't mean "turn")

platform is irrelevant. game type is what matters here.

I am working on a concept for now of a PvP game which would be limited to phones and possibly tablets.

this really is largely irrelevant. whether you play skyrim on a PC or a tablet, its should last a long time. whether you play galaga on a PC or phone, each "round" is typically a few minutes at most.

i'm modeling it after two styles - tower defense and card games.

this is whats important - game type. a phone is just another platform - albeit somewhat less powerful than an alienware rig.

how long it should take is really up to you. who says tower defense should only take five minutes? that's not much of a game if you ask me.

how " casual" vs "hardcore" your game is will probably be the deciding factor. for casual, you want something they can pick up quickly, play quickly, and put down at any time. but as long as they're playing, you want them to be able to continue playing. so a design like galaga with 100 levels is better than something with just 5 levels. insufficient content / gameplay hours leaves a bad taste in the payers mouth, "i got ripped off! its too short!" for something more hardcore, you'll want longer term gameplay most likely, with the ability to save and resume. but since its two player only, playing a longer game - possibly over multiple sessions - doesn't really fit well. i mean, when's the next time you and your buddy will both be able to continue the game?

platform is irrelevant. game type is what matters here.

I disagree. People use phones differently than they use computers or consoles. I might pull up a game for a couple minutes while waiting for a friend, I never sit down to a console for a minute long session. Even 'serious' smartphone games often allow you to drop in and out at your leisure.

While platform isn't irrelevant, it should take second place to fun. If you make a great game with an hour long play time, you'll develop a following who's looking for that. If you make a bad game with a 1 minute play time, noone will play. I do expect the sweet spot for phone games is under 5 minutes.

The quicker a match, the more important fast matchmaking becomes.

That is really good input, thank you all.

To clarify:

• I basically am looking at it as a hearthstone-type encounter. You would be paired up with a stranger (or a friend) and play a game, after which point it's over. However prompting 'would you like to play another match?' would probably work great ... so that people can have a rematch if they both choose to.
• The reason I'm thinking to work within time bounds is so that the game is manageable as a quick game before sleep or before work, or on a break. There might be some in-between activity in game, sort of like hearthstone has of crafting cards and making decks - truthfully the game is very much inspired by hearthstone (without cards though).
• Aiming for casual, not hard core play, but i'd like to have features which would give hardcore players advantage.

Maybe take a look at other games you want it to be like. Like Hearthstone, with games that last maybe 5-15 minutes. Since you're talking about 4 minute games, that could work as a more fast paced and casual game than hearthstone.

I'd avoid anything going longer than 10-15 minutes on mobile. It does depend on genre though. A strategy game is expected to take longer than a match-3 game, for instance... but the general rule is "as short as you can make it without sacrificing the quality of the product" :)