Many people have tweaked the schedule of the flush, so give it a try. You can drink water any time except for 20 min before and after the ES and wait for a few hours after the OO mixture. Use common sense with it and you'll be fine.
If you use real olive oil from California, the mixture will go down better in my experience.
About the melatonin, I would say take it crushed or outside the capsule an half hour or so before the OO mixture if you absolutely must have it.Good luck.
HappyManatee