Originally Posted by dsgtc0408

This should be ok, but it might be a little close if there is a hiccup in the Jetstar flight. The good news is that both JL and 3K operate from Terminal 1 so this saves you from having to move yourself from one terminal to the next.

If you have no check in baggage, when arriving at Changi stay airside and go to the transfer desk for your JL boarding pass - you can then proceed to your gate. If you do have baggage, then go through passport control, collect your baggage, go through customs and then ground side as per normal (this could be as fast as 10 minutes if you're really lucky). Then move yourself to the departure level (upstairs) to check in at the JL counter.