What time is your colonoscopy at on the Thursday? I have had many colonoscopies and I avoid doing any prep that day for fear of not being emptied out on time. Since I have to travel one hour to get to the hospital.
I've always started mine the day before usually around 1pm, but I was also given laxatives as well as pictolax(much better only 2 small packages) highly recommend this one over moviprep. The last time I did mine for some reason the prep didn't kick in until about 10pm at night and by then I was ready for bed and totally exhausted, only to have to run to the toilet for the next couple of hours.
Once its clear running out of you then your done-no need to take more, I find it just irritates my insides.