I will tell you what Lisa V also stated - you have to take it and go right to bed. If you take it too soon, you won't be able to sleep. I take the generic Ambiem (zolpidem). I have been taking it now for about a year.
I take it and immediately lay down to sleep. If I take it any sooner - sometimes even just to tidy up the bedroom, go to the potty one last time, etc. - I won't then sleep well - sometimes not at all... yikes!
I will also repeat another response by saying you have to be sure you are going to get the full eight hours. If you don't, you will have the sleep hangover. I have been known to cut the tablets in half too if I know I won't get enough time to sleep - although I have to admit that just recently this has stopped working so much for me - I need the full dose to really sleep.
Best of luck!