Pc West's evidence at trial indicates that it was less than 8 minutes, probably about 5 minutes. This fits with the other evidence if Jeremy got dressed before making his call to Pc West.
This supports the fact that Jeremy made his call to the police at 3.36am, and not 3.26am..
If Jeremy was on the phone talking to the police for about 5 minutes or so, his call would have been terminated at about 3.41am, leaving him 7 minutes or so to get himself to the farmhouse, and arriving there by 3.48am..