I went through the same process with my Vegas flight last month, as the evening departures from LHR all seemed to be catching delays. I tracked the flight for a fortnight and it seemed to be between 1 and 4 hours every day, which I was dreading given the late arrival and long drive the other end.

But on the day I went, we departed early and landed a good hour early to an empty customs hall. I was in my hire car well before the scheduled arrival.

So dont sweat over something you cant control