I recall one occasion – Leuchars Lightnings, when Q1 and Q2 were airborne, Q3-4 were being prepped coming out of the hangar, when at 0400 the TACEVAL team arrived.
The day progressed with two squadrons sitting real Q; there were more ‘Soviet’ aircraft north of the Faroe's Gap than were in all of the RAF at that time (easier to pass that today).
The TACEVAL team had a quiet day.