Before I post a "help wanted" article, I am wondering how long it would take to draw a few pictures. I'm making an app for a mobile device, a simple one, with a specific artistic style. I'll be specific, but I'd like to know a best estimate as I'd need to know if a single artist can do what I'm looking for or if I have to ask for multiple artists.

1) It's a mobile app. So as low as 480 x 240 up to 800 x 480. I think those are the most common resolutions. If not, they should be very similar. And I'd just scale it for the remaining pixels. Probably just make it the larger resolution and just resize it down.
2) Lets make the quantity limit at 10 different pictures for now, with each picture having a landscape version and a portrait version. So it should be faster to do that than create 20 unique images, I'd imagine.
3) Now the style, I'm not looking for crisp, sharp images. The style is more concept art style... blotchy and ink-like. Here's several wallbase samples I found and how close to the style I'm searching for, that I rated them for. They are not what i'm looking for content-wise, but they are what I'm looking for style-wise:

http://wallbase.net/wallpaper/258602 - pretty darn close. At 100% it might be a bit much, but zoomed out a little, it's pretty nice.
http://wallbase.net/wallpaper/68809 - another really good one. Detail where there needs to be detail and sketchy where there doesn't.
http://wallbase.net/wallpaper/911905 - When a portrait is needed, this is about as much detail as I want.
http://wallbase.net/wallpaper/194322 - Too much detail on the helmet, but the rest is spot on.

With each of those, the resolution is too high but the style is definitely what I'm looking for.

I don't think it's important, but it would be mostly fantasy artwork, closer to guildwars / LOTR than WoW or more cartoony.

Any idea what a time frame would be for these to be made?

The technique is called digital painting, with a bit of impressionist style. Sorry I can't really give you a time estimate though - it would take me personally a long time, but that's because it's not a style I'm experienced with. Just as a rough guess, the fastest a freelance artist could do something like your first two examples would be about two days each, while a week each would be more common for a less experienced artist or one with less free time. A serious professional could probably do it in a day but that kind of person earns a pay rate of more than $20 an hour, not really who you'd want to hire for an indie game.

It depends on the artist.

Most concept artists often practice digital speed painting using resolution independent vector based software (like the Corel Painter series). And could knock any one of those examples out in a couple hours.