Multi-park ticket

by Loany
(China)

Visiting Singapore from Oct 12 to 16th with friends. Have days free to visit the Zoo on days 13th and 15th. Interested in the Multi-park ticket but doubt all parks can be visited on a single day (without running).
Questions:
1- Do multi-park tickets expire on the purchased day, or they can be used on different days? (so we can divide the visit of two parks in one day and another two parks later).
2- If valid for a period of time until used, how many days would that be? Would it cover our staying (from 13th to 15th is 3 days).

Thanks in advance for your time and help,