I have had three colonscopies, here is my advice, but I am not a doctor, and every individual is different.
1. Have the colonscopy done in the afternoon. The prep is much easier, especially concerning fasting. You will be fasting mostly over night. You will be able to eat one time the day before in the morning. If you have a morning colonscopy you fast all day the day before. Once you start taking the medicine, assuming you are taking the liquid, you must stay near a bathroom. So, if your last meal is breakfast and then yiu start meds in the afternoon, you could go to a class in the morning.
2. The day you have the colonscopy you absolutely cannot plan on anything except finishing your prep (which includes being in the bathroom) going to where you are having the procedure, and the rest of the day you will be too medicated to do anything that takes real attention. You cannot drive, you shouldn’t plan on studying, making important decisions, nothing like that, you will be somewhat impaired.
If you are taking pills like ducolax for the entire prep and not the liquid, those pills take about 6 hours to start kicking in but do not cut it close, because once it starts it is big time living on the toilette.
I personally never take the entire prep. I figure they give the same amount to 220 pound men and I am 140. @Rarebear could verify if that is true or not I am just guessing. I assume @Rarebear will not agree with me to adjust your dose though, and you do risk not getting cleaned out well enough if you do. I have never had a problem and I usually take about ¾. I can tell once everything coming out of me is coming out basically like yellow pee that I am cleaned out. But, the first 12 hours you might get that way, but then after some rest and you start taking the second shift of medicine solids can start coming out again, so don’t stop halfway and not start up the meds again. If you take certain drugs it can make yu more constipated and harder to clean out, like if you regularly take narcotics, and then you need more meds then the average person.
The doctor will provide you with the instructions for the medicine, you can ask if he has different schedules for morning or afternoon procedures if you think one will suit you better and compare them.
If this test cannot wait I assume there is an immediate concern. I think your professor will let yu take the test a different day with one of his other classes.