Ok I went out on the flats here in west fla during the day and was amazed at how many shrimp there were. They were about 2" long and looked tasty, not enough to make a meal as my time was limited. I'd like to explore this a bit more and find out some more info on best time of year, tides, moon, links for info, etc.. Thanks!
For large shrimp - late September, October, November. They will tend to be in slightly deeper water (large creeks, bays, etc). Check to see if you can bait the shrimp (fish meal or dog foot mixed with clay or mud into balls, then let dry.... they will stink something fierce). Toss balls around marked polls (you have to be licensed to bait shrimp in SC - where I used to go), wait 30 minutes, then troll up and down your line of polls and cast.
I'd say August and September, you can catch them further up in creeks. Generally best when the tides coming in. Moon doesn't matter too much. Although light attracts them to the surface a bit.
You can fill a 48qt cooler in a few hours on a good night!
Cat food in cans work good too, just punch holes in cans to let out the food and scent. Here on the East coast in the summer we will find a sandy beach in the river that has calm water with drop off near by. We go at nite on incoming tide. We use lights on the beach, it seem to attract the shrimp. Fish meal and clay balls we used most of the time. We have had some good nite of the beaches here catch about a havea five gallon bucket full, sometime allmost a full bucket. in some ares U can catch a crap load out of boats more inland in brackish water.