I'd say about 2 hours after "lights on: you should be able to tell. Mine retract after dark and usually are fully opened by a couple hours after lights on. I work a swing shift so I don't see them till after 10 am here (lights ramp up starting at 8 am).
Try and mimic the flow you see in my tank if you can. Just that slow gentle motion. I understand that may not be 100% realistic, but do your best. If they look like a palm tree in a hurricane, you have wayyyyy too much... lol
Notice ALL of mine are right off the sand? Notice I have a few back near the back glass under a rock overhang? All of this is to minimize what is otherwise a pretty heavy flow over the rest of my tank.