You could arrive at half 12 if you want but the lounge is pleasant enough to while away an hour or so beforehand. Passport control is done centrally but security is at the gate, so it's largely a 'we won't leave without you' situation as long as you're in the gate queue at T-20. There's no fast track at that point but if there's another flight leaving afterwards from the same gate area (which there can be) you can get away with pushing in.

Note that because of the gate security, you can't take any drinks bought in the terminal onboard. Only sealed duty free.