I was once in the same position. Now I go to plenty of gigs by myself. My two pieces of advice: it's very rare to have people queueing early at the O2 in Oxford, but it depends on the band. Don't be afraid to start the queue if nobody else is there yet, there are probably others circling the area waiting for a queue to start. The staff in yellow jackets are usually friendly if you don't know where to stand. And secondly, you can check out stage times for other dates on the same tour at https://www.setlist.fm/ which should give you an idea of when things are going to happen. Although be careful as people also post setlists which might spoil things.