You want to see signs of rain when you wake — puddles that weren’t there the night before, maybe wet streets. You don’t want it to have rained too early in the evening. Sometime between 11 p.m. and 3 a.m. is best, though later still works.
You want the birds that left Cuba and parts south just after sunset to have hit the weather over the Keys, to know their migration was done for the night, and to set down.
You want it to rain enough that, after the birds have given up on the evening’s long-haul flight, they don’t keep moving forward on short hops.
That’s how it works in my head, at least....