The flushing protocol schedule as described by it's author is that way for a reason. It is said that the body starts certain processes at night so the cleanse is designed to take advantage of this. Most authors of the various flushes agree on these relative times, and it is to be derived that a better flush would occur.
That being said do the flush at any time you want and report to us as to how it goes. Most are not brave enough to bring a report, for we do not want to drink the vile concoction in vain and risk a poor flush so like automautons we pretty much stick to schedule.
If I were you I would try a few as prescribed and then add your own deviations so at least you have a form of comparison. I deviated greatly in my flushes that equal my age because I have a feeling of what is occurring.
Never has there been a butt pee issue in bed. The sleep/rest has generally been some of the best because of my intent.
Oh yeah at least one flush I know of is done during the day whilst walking around. It was Dusan's grandma I recall.