Originally Posted by NWIFlyer

Much depends on where the OP is sitting on the plane, whether they have status, whether their passport allows them to use the e-gates for a landside transfer. Ordinarily these things don't matter to most passengers, but here they potentially become crucial.

Best case scenario assuming exactly on-time at the gate, airside transfer: 6.22 off the plane, arrival gate close to the transfer buses (I think the best option here - immigration is less predictable and the walk is fairly long in the landside tunnel), arrive transfer bus at 6.27. Bus arrives at 6.30. Arrive T2 at 6.35. Transit security by 6.40. Clear security at 6.45. Gate by 6.55, so 15 minutes to spare before gate close.

Landside transfer: 6.22 off the plane, arrival gate close to immigration. 6.25 at immigration. 6.30 exit immigration. 6.35 exit T3. Walk landside to T2, using lifts at T2 to departures. Arrive T2 departures 6.45. At security 6.47. Clear security 6.50 (highly optimistically, even the priority lane isn't quick these days). Gate 6.55.

In reality, this ideal will not happen and there'll be another 10 minutes lost somewhere. It really, really wouldn't take much for this to go wrong.