Bioshock 1/2/Infinite, and Halo 4 won't take you very long at all, if you are somewhat proficient at video games, especially if you choose to play Halo 4 co-op. Dragon Age 2, if you do all the side content, I imagine it will take you longer than the other games. If you beeline through the story, however, you can complete it relatively quick.
If you wanted an estimate on each based off someones personal play throughs..
Halo 4 Legendary co-op with 3 people took me just over 6 hours. Bioshock one my first play through took about 8 1/2-9 and Bioshock 2 took about 10-11 hours.
Combined, all 3 games if you press through them should only take about 24 hours worth of your time. Judging on how much you play Xbox on a daily basis, 3-4 hours a day, a couple days a week and you'll be through them all within a week and a half, two weeks of you play regularly.
Gamertag - GotMyProSocksOn What you think is broken with a game could easily be explained with you being terrible at it.