but on a tournament flier I am working on; I set up rounds 1 and 3 with fixed start time.
Round 2 and 4 I told the participates to stay around so we can start early, if possible. Yeah I know herding chess players is like herding cats.
Round 3 is the round after lunch. One day tournament
Anyway just a suggestion
For Hexes and Quads, I usually say “Rounds x-y-z or earlier by agreement.”
Herding cats sounds about right.
You will need to post the start times in several places on the day of the tournament:
Start times
Round 2: ASAP
Round 3: 1 p.m.
Round 4: ASAP
No one will remember it from the flyer. Even if you post it, some will not see the signs and ask you when the round starts after lunch. Others won’t ask at all, and arrive late for the start of the third round; but you probably won’t get a major gripe about clocks getting started on a late player. Past a point, cats accept the consequences of behaving like … cats.
Also post it right next to the score reporting form.
The most effective place I’ve found to post round times is on the door of the bathrooms.
Sorry, doesn’t work.
Aha! 
That one I haven’t yet tried, but will next time around. I’ll let you know how it goes.
One thing I did at one tournament was figure out the pairings as soon as possible and then allow players to start early if they were both there and wanted to. That gave a little bit of the effect of ASAP while still allowing people to keep to leave to grab an early lunch if they wanted to do that rather than hang around.
The tournament ended up with a one-hour lunch break that had not been originally scheduled with the exception of one game that was played at the original round three time (for a player that had a planned round two bye and wouldn’t be back until the normal round three time in the five-round Swiss).