HOOB747 wrote:Sure, plenty of time. SIN is super-efficient for traveling on separate tickets. You should be fine.
Not so, Air Asia has recently relocated to Terminal 4, without connection with other terminals via skytrain or air-side transfer.
So you need to clear the immigration (I assume from Terminal 3), take the shuttle bus (10 mins ride, headway 15 mins) to Terminal 4,
then check in and pass the immigration again at Terminal 4.