Departing LHR tomorrow 3/23 United...Int’l flight departs 0920, boarding begins 0830 and closes 0905. We have Priority Board and are group 2

We are staying at Novotel T1, 2, & 3. Hotel says takes 10 minutes by cab so 0530 is enough time to get picked up and go through security.

I’m asking this because on arrival last week we stood in Immigration line for 2 & ½ hours so I’m wondering if this is any indication of time needed to depart to U.S.? Should we allow more time to arrive at terminal 2 and get through security?