Why would he go home and then return to stay the night ? Was he missing his mum and dad ?
Given that he didn't finish the work in the fields and left his farther to bring in the last trailer full of rape seed (or so he said), they MAY have argued over him going home before completing the job. BW said that Nevill sounded as though he had just been arguing with someone - so. being pissed off, Jeremy goes home and calls Julie "tonight's the night". He MAY have decided to return to WHF on a ruse of making things good with his dad. That gets him in the house, so no break in required. He returned anyway, we know that, it's the time he returned that's in question but once inside the house and with the bonus of not having to sneak around, he was in a much better position to corry out the plan.