In Florida, there are spring and fall runs of redfish that group up on the flats and this is an excellent time to target them because of the quantity of redfish all in big schools. That being said: there are also many redfish to catch all year long around oyster bars, mangroves, docks etc... But if I were to go looking for redfish on the flats, the best time would be at the lowest of tides.
The reason is that where there is no water where redfish usually hang out, the fish obviously aren't there. That leaves the fish to be found only in the few areas holding water: flats! I'm sure you have heard the term "tailing redfish". This is when they are digging around in the shallow water looking for food, so their tails are sticking up out of the water. So, when you put some food out in front of them, there's a good chance they will eat it.
If you had to fish when the tide was high and up, your most likely to find redfish back in the mangroves or up over and around oyster bars. Fishing in different areas will have different times the redfish will feed best. So the best thing you can do is start to log your trips. This will let you pattern the redfish, learning fast which times in which areas the redfish feed best.
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