FI.
In my airborne experience of flypasts and parades, there are really two main timing methods. Either, the flypast occurs at a fixed time or, someone co-ordinates timing updates from the ground to the lead aircraft. The fixed time method seems to work more with the large formal flypasts, usually cast in stone and the co-ordination is done by a worried looking chap who gets the ground event to the correct place at the right time.
OTOH, events such as BoB drinkies and AOC's will have a nominal timing but, the participating aircraft will normally be in a timing hold about 10Nm away and should be able to adjust to suit the call from the guy on the ground.
Tales (experience) of cock-ups in the air are comprehensive and, make me wonder why I got duped into doing so many!
OAP