STATIC PROGRESSION

I am slightly confused. In the book, it says that if you can hold a static position more the 15 seconds, you can move on. Thatsfine with me, i moved onto advance l-sit becasue i can do an L-sit for thirty seonconds. But why do i keep seeing people say that 3x30s is best. Do i have to do that before i progress? or is that just something i can incorperate into my work out. I have tried to see if this questionhas been answered already bnefore i posted this but i could not find it anywhere

On many different posts, Coach and others have pointed out that a 60 second, or 3x30s L-sit is a fundamental thing to learn. The learning curve should be that for the first variations, in let's say front lever, you should do a 60-second hold before trying another one. In case of said front lever, 60s tuck -> 60s Adv tuck. After that, only 15 second holds are needed - although it doesn't hurt to be able to do a 60s full lay hold

ohhh!!!! makes much more sense now! back to l-sits then!