The first time I did this I was not confident because I thought I let it stay in the cooler too long (and I had never done this before). It was wrapped in foil, wrapped in a bath towel and in my Kodi cooler sealed up for 8 hours. When I took it out to cut it was practically too hot to hold with my hand and had to get insulated gloves. One of the best danged briskets I've ever had.
A big piece of meat (that's what she said!) has a lot of heat energy, and insulated from heat loss via foil, towel, and cooler, they will stay hot for a long time.
For a brisket, 3 hours is probably a minimum amount of time to rest, to fully break down all the fats and connective tissues, and all without the risk of drying it out as there's no additional heat being applied to the meat via the grill.
Going to cook salmon tomorrow. I use a cedar plank on the grill to get indirect heat, and some good smoke flavor into the fish.
Season up the fish, put a couple of pats on butter on it.
Grill to 400 F, no heat deflector.
Soak plank in water for 15 minutes, then onto grill until it's lightly smoking.
Fish on, for 45 minutes. If the fish is thick enough to use a meat thermometer that's the way to go, otherwise check after 30 and keep cooking till it's tasty. With the indirect heat, there's more of a window from bait to dry as dust, than with an open fire.
Previous grouper work: