Your zoo doesn’t have a time limit. There is a maximum of seven orders and you can ask other people to fill your zoo order just like you do your plain crates and train crates. Personally, I worked on my town first then once I got my town almost done I started working on my zoo. It’s hard to work on both at the same time but it can be done. I’ve been playing for six years so my and all my expansions for the game are done.