On Sunday, gates will open at midday. The music will start around one hour later and Stevie Wonder will be last on, finishing at around 10 at night.
The main stage times are on http://www.callingfestival.co.uk/line-up/stage/main-stage and the Pepsi Max stage times are on http://www.callingfestival.co.uk/line-up/stage/pepsi-max-stage.
The trick, for me at least, is not arriving so early I get over relaxed before the main event. How does aiming to get there to kick off with Paloma Faith sound? She is on at twenty past four, so maybe aim to arrive around ten to?