Well you have time so why not try it out. If they reject you at T3 connections can't you just go back to T5? Why would you exit through the border?
I’d have to get my boarding pass reset and kind of assume that would be easier at First Wing (after going through border in T5). Plus it will certainly be quicker at FW vs security at flight connections. Only question is whether FW will still be open at 6pm.