Logistics of SQ to JL Connection
 

I am planning a trip on two separate tickets on SQ with a onward connection onto JAL.

The connection time is 2hrs around midnight. We will not be checking any bags, and will be flying in business/first class.

Will I have to go through immigration to go from T3 to T1? Looks like we can take the skytrain from Terminal 3 to Terminal 1.
Is there a transfer counter for JAL inside T1 that would be able to provide our boarding passes?
Is a 2hr connection time at Changi on separate tickets enough time? My SQ flight arriving at Changi has a great on-time performance.

Because Changi airport in Singapore has ONLY international connections, and because security screening is done at the departure gate, you just walk from your arrival gate to your departure gate. There are also some airside trams to go between selected terminals. There is NO immigration screening whatsoever. If you don't have your on-going boarding pass, you can get that issued at the airlines transfer counter. so a 2 hour layover should be no problem. It won't be much different than a domestic layover in the US at Denver or Atlanta airports.
When you arrive Singapore there will likely be an SQ agent at the gate to greet and help arriving passengers. Just check with him/her.
Changi is one of the best airports in the world.

Thanks that puts my mind at ease. Hopefully we have a chance to check out The Private Room also.

Just one thing to bear in mind is that if you happen to arrive at the furthest gate away from the sky train in T3, and the departure gate is the furthest away in T1 you will have quite a walk so if you do arrive slightly late, it might be worth putting your skates on, so to speak.

Good point.

We'll also try to get an onward boarding pass before our incoming flight into SIN. Hopefully the JL agents at SYD will allow something like that.

When is this trip? I'd be interested to hear how it worked out for you.