You can check in at the AC. There's no need to go to flight connections or thru any type of security (except at the gate.)

Get off the plane, run to the AC and run back you could do it in 30 minutes but flights close 30 minutes so although you could do it physically you couldn't do it operationally.

If you are not a AC member or in C or F then you do need to go to flight connections in whch case you can do it in 30-45 minutes. Security between T3 and Flight connections is minimal.