If he doesn't get cleaned out, they'll have to redo the test.
As far as it being late in the day, we frequently start colonoscopy prep late in the evening for a morning scope. Granted, the patients don't really get any sleep and are up most of the night on the bedpan or commode, but ICU patients rarely get a good night's sleep anyway. :( We'd start them earlier but we usually do scopes for GI bleeds and illness doesn't just happen 9 to 5.