Interesting take on this... I didn't even think about getting day tickets AND night tickets and just staying... that might actually be a super convenient idea and esp if they let you in a little early! I'm mostly interested in seeing the pangolin, tasmanian devil, hyenas and doing the rhino feeding for $10 during the night safari.
Sounds like using the subway to get there is easy enough, and then maybe we'd just do Grab back to the hotel after.
Have you or
@sky13 done Windsor Nature Park? I've also read good things about that, appears to be free, and seems to be in the same vicinity as the zoo. Mostly would be interested in walking around trying to see the monkeys, and see other wildlife.