With my ex, he was always done in a few minutes, except for the one time he was sick and we fooled around anyway. Not that it really mattered because I'm quite an easy customer when it comes to the orgasms.
With the current beau, I haven't really bothered to time it but it's definitely a lot longer than 5 minutes. I honestly don't know if it would be physically possible to have a quickie with my current boyfriend. Not that I'm complaining....
impulse03 - Living with roommates sucks like that. If it's a viable option, save up a few bucks and find your way to a motel for a night. There will be less stress on you and your girl and you'll be able to relax and enjoy yourselves. Otherwise, I wouldn't worry too much about it. Trying new things is half the fun anyway. Don't be upset if it doesn't work quite the way you imagine the first time.