How late the night before a 2:30 pm colonoscopy can I take the 1st dose of Suprep? I won’t be able

Follow the Suprep instructions exactly. If you cannot start at the scheduled time to take the Suprep, you should be 24 hours food-free and have the Suprep done. Food free for 24 hours is a normal practice. I do not know your scheduled time of colonoscopy, so it's hard to say how late you can take the 1st dose. Consult with the doctor if you fail to take the dose at the scheduled time, he should be able to make some adjustments for you.