I would say in early April get the heat pre-paid for sure.
We still turn ours on even in May, but we like our pools warm.
Also ask if the home has a pool blanket, if not, you will lose all the heat in the pool at night.
Some owners and MCs will let you pay for it and turn it on when you arrive...but it might take a day or 2 for them to turn it on...and then it's going to take another day to warm up. I would much prefer to just have it already warm when we get there, and we've read quite a few posts here on the DIS of people saying they wished they'd had it (of course there are those who don't want it or don't care too). Now, it all depends on how warm it is in Florida then too of course...and that's the real variable here....or unknown.
Most of the pool heaters are a heat exchanger, meaning they pull heat from the atmosphere. They don't work when the temp falls below 55 degrees...which means at night they don't heat at all (another reason you need a pool blanket).
You can set the temp of the water on the heaters..but 75-80 degrees is a "common" setting for most people, nice and warm!
My suggestion is to go with pool heat in advance!
