And just to throw on to staying at the airport, there is a movie theater and quite a few different things to do/see. Check out:
16 Secret Things To Do At Changi Airport That Will Make You Want To Visit Early - TheSmartLocal
One additional thought, are you a 75-night SPG Plat? Not sure what the benefits will be post "Merger" this weekend, but you might be able to make use of the Your24 benefit. It might allow you to check-in very early and since your stay is less than 24 hours, you don't have to worry about check-out time.