Depending on what time your flight leaves the next morning, you might be better off simply staying in the Transit hotel at the airport. Its much cheaper than Hyatt (or most other hotels), and it will save you time. You can get into the transit area easily with your ticket if you are flying on SQ, since they allows checkins at almost any time. If not on SQ, then you might have trouble getting into the transit area much earlier than your flight.
For a huge cost savings, the YMCA at #1 Orchard Road is cheap at something like $60/night. Rooms are decent, and the location is as good as the Hyatt.
For night shots, I'd do:
1 - City shot at night (I've seen people take this on the ECP highway, just below the Ritz Hotel, but not sure how to get there. There is a walkway along the highway.)
2 - Lau Pau Sat (probably the best hawker center to take wide pictures, since it is more open than most centers)
3 - Suntec City Fountain--largest fountain in the world (have to check to see if it is running)
4 - Boat Quay (water and restaurant shots)
5 - City shot from the top floor of the Swissotel Stamford (tallest hotel in the city and their is a bar at the top, where you could get photos of the city and have a drink!)