I've used it twice and both times, I have done both doses the day before. First dose at 4:00 pm and the 2nd at 7:00 pm. Both times I've only managed to get down 1/2 - 3/4 of the 2nd dose. I just couldn't bring myself to finish it. I have had no complaints from my Doc about
not being totally cleaned out even though I didn't finish. You know when you are clear. I don't think I'd be comfortable taking the 2nd dose the day of my colonoscopy unless I was scheduled to have it done in the afternoon. I'm too hungry to go without food that long so I like to try to be the first one of the day. It's horrible, but you'll do fine.
Oh, besides tasting horrible, the prep was fine. I didn't throw up, no cramping, and no prolonged bathroom time. 4 or 5 trips to the bathroom after each dose, then I was done. I was able to sleep all nite without having to get up multiple times.