How long does it take to get in on saturdays? At what time can or should we start lining up??

First of all, if I would purchase the tickets on line, cause once they've reached capacity they close the gate. Then the sooner the better

The earlier the better. Once the park meets capacity, whether you have a ticket or not, they will no longer admit anyone in.

You should arrive by 9 AM recommended if you want to try all the rides.