Colonoscopy and PEG-3350

[PEG3350]

I have a colonoscopy scheduled for 10:30 a.m. (arrival time at clinic) and I was instructed to start drinking the first half of my 4L PEG-3350 preparation at 6:00 p.m. on the day before.  The second half is supposed to be taken early the next morning.  

Here my problem:  I have some scheduling difficulties and my life would be a lot easier if I could start drinking the PEG at 8:00 p.m. on the day before instead of 6:00 p.m.  Considering that some people are scheduled for colonoscopies at 8:00 a.m. and those people are also instructed to start drinking the PEG at 6:00 p.m. the day before, it seems like nothing should speak against delaying the PEG intake by two hours.  What do the experts say to this?

Thanks in advance!