@ojo
Actually, you will be in the exact same situation. You are doing exactly what we did - flew SIA into Singapore, connecting to an SIA flight to Jakarta (easy connection, great airline). We had that same 6 hour layover, 6PM-12AM...
You will use <an hour to clear customs and get through immigration (even getting a visa on arrival - much easier in Jakarta than in Bali). We walked our bags to the check in counter (upstairs, not a long walk, but longer than "short"). At this point, you have a choice, go through security, etc. and enter the air-side of the terminal. It sounds strange, but there is nothing open (this terminal is used for morning flights, so all the shops close early evening). It may be the quietest terminal you've have ever been in... Everything is closed but the KFC (which wasn't horrible
Now, instead of going straight through security, if you stay on the land-side after check in, there are a few other food choices available (I'm assuming they are open, I've only eaten there mid-morning to noon...).
basically, the wait for the flight is very comfortable and quiet, just not not lot of stores open during the time you'll be there.
Our learning was, if we do it this way again (and we may, next year), we'll bring food for the wait.