Gymnastics Workout of the Day
If you sign up to the athletics log, you can look at some of the more gymnastics workouts and pick different ones that may not be so CrossFit like.
A bodyweight crossfit workout like "Cindy" may be good for you. A round is 5 pullups, 10 pushups, and 15 squats. The goal is to see how many rounds you can do in 20 minutes.
I would reccomend trying this at first for 10 minutes and focusing on good reps and not killing yourself. Scaling back. You can also scale the movements back ( jumping or swinging pullups, pushups on knees, hopefully you can do a squat but perhaps lunges instead or fewer squats ).
The only way you're gonna get used to 12 hours is by doing it for about 3-6 weeks. By week 3, you'll be a lot better than week 1 and you may notice by week 2 it isn't so bad. Make sure you are eating properly (?!) and sleeping and hydrating enough.
It would be a good idea to create a basic warmup, practice about 20-30 kick to handstands and about 1-2 minutes of total wall handstand time. This will depend on how what shape you are in now.
Work on a bunch of bridge stuff as well.
Work some pullups, pushups, leg lifts, and lunges/squats.
Stretch the first week 2-3x and if you can up that to 3-4 times the second week. 2-3 will be fine if the stretching leaves you too sore ( it takes time to get used recovering and working out ).