You drink Olive-Oil mix for example on Saturday evening and recover on Sunday.
You can do it whenever you have a day free ahead. Just make sure you follow Clarks recipe to letter as for eating and drinking regulations on the day of flush. I sometimes did my flushes on Fridays, drinking my epsoms in the office.
Some feel very energetic next day after the flush, but the problem is that in any case you will have to run quite often to toilet, untill around 2-3 pm, that is why it is important to have day free after the night with Oil (that is the flushing night). Even if you feel very tired on the next day after flush, next day you will feel O'K.
Best way to regain strength after flush is to make sure all "flush product" is out of you (do enema if are not sure that epsoms washed your intestines totally). And intense rehydration. Drink a lot of water.
I have never used Ornithine in my flushes and I don't think it is really that necessary. You don't have to sleep if you don't feel like, just stay in rest. Watch tv or read a book, for example, or do some home work that does not require much motion.