I would...
After landing @ 1730, you should be in your hotel checked in by 1830 - 1845, ready to head out by 1900.
A 1/2 hour taxi ride will get you to the night safari (I have been 3 times now) - excellent entertainment:
NIGHT SAFARI
Following the safari - taxi back to newton circus hawkers centre for a meal -
NEWTON CIRCUS - see Mrs ?? (help me out here oz_mark, at stand 70
oz_mark in the clutches of the stall holder - great food, great service - great prices!
I would then taxi to Clarke Quay and enjoy Pump till I needed sleep:
Pump, this is one of my FAV night spots in Singapore - caters for young and old! (er)
Next morning, I would be up and about and head into little India for a look at the
Mustafa Centre. I would then taxi to China town, and spend a couple of hours wandering the back alleys looking at the antique shops and speciality shops. There's a building close where on level 2 or 3 there's another hawkers centre, that would be my destination for lunch for a Malaysian inspired lunch.
After lunch, I would head to the singapore flyer - this is a good waste of an hour or so, and what a view from 165 meters up -
Singapore Flyer.
By the time you have resurfaced, it will be time to collect your luggage and head out to Changi.