It's been about a year since I used Impossible film (will use it again in about a week), but yes, you should see something in less than 5 minutes. It will take a while to fully develop. This is a bit annoying, though, when you are trying to get your exposure right - you have to wait some time before it is done enough to see if you need to play with the lighten/darken control.
I know it's pricey, but consider your first couple packs as experiments. Also, this stuff doesn't keep as well as the old Polaroid film, so shoot it within a few months of getting it. Otherwise, the chemicals may not spread evenly or completely.