Hi IrishPilot
Florida is a great place to do your hour building im sure ull enjoy it.
Dont worry about the US immigration, unless uve done something wrong in the past, they wont deny you access.
They will chat to you, and ask you why you are going to xxxxx (they already know where you are staying, its on the computer) just tell them you have a private pilots license and you are there on a flying holiday.
Ive met loads of people who get worried about going through immigration. Really there is nothing to worry about, ull be through in a couple of mins!
One bit of advise is, DO NOT LIE, if you are there for hour building, then tell them.
Enjoy your time there.