Fort Pickens is National Park Service - 14 nights at a time - 2 nights out between stays - and no more than 14 nights between March 1 and Labor Day - no more than 42 nights in a year.
The COE sites are also 14 days - but you need to check with the individual CG - some allow longer stays in the cold weather months.
Salt Springs has a 180 day stay limit for some sites between Oct 15 and April 15 - but you can only reserve 21 days on-line. Currently the Salt Springs sites are all listed as walkup only. Need to call the park if you want to stay longer.
What I read is that it is very crowded this time of year.
There are a lot of seniors who do the 14 day shuffle between to COE campgrounds on the same lake. Burns Run East and Burns Run West are popular on Lake Texoma - about five miles apart and 50/W/S is $24 regular / $12 senior pass - 30 days camping for $360.
Some months the electric bill alone for my home near Dallas is that much.