It varies, but of course they have to have room to swim or escape. Sometimes they'll be in the wake of boat traffic - they're very curious, playful critters!
We've spotted them at all times of the day but more often in early morning or late afternoon/early evening ~ don't know if that's coincidence or what. It probably depends mostly on where their food sources go! Ya know, they eat FAST food
! (sorry, couldn't resist the pun!)
P'Kid will tell you that the surest way to see dolphins is to take a "dolphin cruise"! When my hubby and I lived (and had a giftshop on the beach) in Daytona Shores, we'd look through the binoculars when the Critter Fleet Cruise went by and saw lots of dolphins following the boat! That was really cool!