There is no expiration unless:
1) They are Star or Advenuturer tickets (they will be labelled with those names) These tickets have days that must be used consecutively so if you used one day, they will expire after the 2nd day. If you haven't used them at all, then they won't expire.
2) Your tickets are buy one or two days and get extra days free (such as 2 day/3rd day free or the Bonus tickets 2 days/ get 3 days free.) These days also must be used within a certain time frame. If the ticket hasn't been used at all then they won't expire.
3) The tickets are comp tickets (employee complimentary tickets or some other comp tickets have expirations) These tickets will have printed on them an expiration date. If there is no expiration printed on the comp tickets then they won't expire.