If ziplining isn't your thing, the entrance just to see the animals is $10, and hostel guests get $1 off of that (it's been my mission this year to try to line up savings for hostel guests at various businesses near us, so staying at the hostel can save you some $$ and make you feel like a VIP :) ).
Mayan Jungle is closed on Saturdays, and any other day, you should plan to arrive before 3pm.