No matter what time of year it is, we always have guests swimming in the pools ! It definitely depends on where you are from on what you consider chilly to be, but we do heat the pools to about 80°F so at least the water is warm. If you go swimming or not, that is up to you.
Coming from Fl I won;t get in water until its in the mid 80s at least (yeah spoiled) unless the temps are really warm in the pools - 'heated in 70s' is too cold for me, but not the kiddos). However I second the hot tub - what a lovely relaxing, muscle massaging way to end the day