I started once very late, like 9:30pm to take the ES and then 11:30pm to take the OO (Olive-Oil)
& grapefruit juice. I did great, and it just made the day longer where I was passing stones.
I still took the next day off, and just laid around and read or slept.
I think that it's probably always good to try do the times like it says, but if you really need a flush and that's the only way you can do it, (if it was me), well, I'd try it and just follow as close as I could.
I'm sure that throughout history, people have done this in varying ways...this is not a new recipe. It's older than timepieces, I'd bet!