90 days is a long time. If you're only doing one team then you will have no trouble at all if you spend time doing instances. People are reaching 60 in around 2 days played, so even if you're only getting 10 hours a week played time that is still only 6 weeks, leaving 30 hours you could run instances. And that's a worst case, because none of us spend as little as 10 hours a week playing.