Static holds for time.
This info is Chris Sommers from the Gymnastic bodies website.
His guidance for static holds was to aim for a 1 minute hold. If you could not hold "X" amt of weight for 1 minute then do static holds until your time added up to 1 minute. When you could do a hold for one minute, then it was time to make it harder. He says that longer than 1 minute and your building endurance, not strength.
You can incorporate holds into a lot of other moves. Chins, hold in the up position. Flyes, and I love this move. Feet off the floor, and held out in front of you elevated, then hold in the down position. Even if your doing regular style flyes, put your feet out in front of you, and hold them elevated.
Read this article on doing planche's. Then try to hold even the basic "Frog" position for 1 minute. Try to even hold a basic tuck planche for any amount of time.
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