corporate-wage-slave

I don't think they will let you into the building that early, formally I think it's 3 hours, and they may let you in at 4 hours, but 6 hours seems too long. There is a rather odd waiting room with basic seating in the next building if you arrive early. You are better off finding a hotel in the vicinity, having a good slow supper there then moving to the airport nearer midnight. MMB should also give lounge guidance, but if not it's Plaza or ITC lounges, both comfortable in terms of seating if they don't get too crowded, but 2 hours would be boring enough I would suggest.