Do you have to buy a ticket for a specific day or do you just buy one and the show it when you want to go?

The tickets are not tied to a specific day.

You can buy tickets online and pick it up and use it at your leisure.

You can purchase tickets at the box office anytime the park is open

We had a 3 day San Diego pass, once started it is valid for 3 consecutive days.

I know if you buy a ticket on line (like thru AAA) ticket is good for one year