Well... Ibis' question does quite make sense...
As I have seen, what you say is correct, more or less, Malone. I mean, when you create a mission, you will have no problem with the time indicated on the waypoint as long as the concerned planes are airstart. But, if they start from the ground, having to take off, things are changing. They will need time to take off (and the more planes have to take off, the bigger will the delay be), and this is not implemented in the elapsed time counter.
As long as I know, the best solution until now, when you create a mission, is to play it to test it, using the autopilot. This way, you will see if the rendez-vous are OK or not !