Assume you will do OLCI. I would say 5:45 - security is a zoo at that hour, so you need to leave 20 mins even if the priority lane is up and running. Total of 10 mins to get through Nexus/get to gate; 15 minutes backup if you get sent to secondary; that gets you to the gate with 15 minutes to spare. But that is really pushing it. 5:25 gives you a much better margin