I have 2
and they take about 30 mins to fully melt, but since they drop the water 2 to 3 degrees it takes another 4 to 5 hours max for the water to come back up, and when i put them in the lights are only going to be on another 2 to 3 hours so its usually ok.
my light schedule is 1 to 9, i get home at 5 , throw the chillers in (only if i have to mind you), then take em out whenever i get around to it.