Sheepshead are one of the few fish inshore that will bite well through a slack tide. They are also willing to bite throughout the entire day. You just need to find them and present a bait to them that they want to eat. Some anglers do report a better bite in the mornings and evenings from spring through fall and a better bite sometimes occurring during the middle of the day in the winter.
However, if you’re looking to go fishing for sheepshead, don’t let the time of day affect when you have to fish. Go when you can because there should always be some sheepshead feeding somewhere. Find them and get the right baits down there and don’t let them steal your bait.