I believe it was probably so but I don't know for certain what time others turned up or what the procedure was first thing in the morning though I presume Jeremy would turn up and go straight into the farmhouse but not ever having been there at that time in the morning or any other time I cannot be absolutely certain.

In all likelihood there would have been someone who worked at the farm before Jeremy usually arrived.
This is bad in the sense that Jeremy has no alibi. Saying he was home alone sleeping is not a solid alibi if they suspect it is murder.
His frame job featured making an alibi of sorts by saying he was hope to receive a phone call and making sure police saw him arrive so they would not think he was there and had phoned from WHF then walked outside.
His frame job also placed the blame sqaurely on Sheila to try to cast suspicion away from him. Instead of just leaving the rifle on her he went out of his way to suggest she was responsible.
Had he simply left her body seated where she died, have taken the suppressor off before killing her, had not made up the story about the gun lacking the suppressor, had staged a box that had at least 5 less bullets and not had told Julie so much he would have gotten away with it.