I called Ginnie Springs about camping. You can reserve the campsites for campers and electric but the non electric tent sites are first come first serve unless you have a large group. Check in can be as early as 8:00am when they open. Check out is sunset of your last day according to there web site.
I will try to get there Fri between 9 to 10am breaking camp Sun early am to get to Blue Grotto before 8:30am when the Dive Rally resumes.
The Rally at Ginnie Sat does not start until 1:00pm leaving time for a morning dive.