I looked around in this thread a bit but didn't find anything fitting.
If one is arriving at Terminal 2 and flying out of the same Terminal, does one have to go through immigration or not? Handluggage only, no checkin.
What's the minimum time you'd recommend between arrival and departure?
If you're going out to another international flight, on the way to immigration, there's a security check and an escalator that brings you up to the departures level so it should be a quick 5 mins walk.
If you're transferring to a domestic flight, then I'm less sure. I was in CGK in early Nov and they seem to be renovating the bit that linked the domestic and international piers including the immigration desks that used to be there so you would probably have to clear immigration with everyone else and walk over to the domestic side of terminal 2 from the outside. The lenght of time this takes depends on how long those queues at immigration are (I arrived on a 4pm SQ flight and took me nearly 30 mins to get out).
Hope that helps.