Glekichi, if that happened at Miles, maybe the 'non compliant' aircraft left early because there were other aircraft inbound? If no-one on the ground there is co-ordinating arrivals and departures, what should one do? Sit there, knowing it forces the airborne guys to hold, or take a punt and get out of there?
Every time we have been running late and called flow control they just tell us to get airborne asap and suck it up. Inbound to BNE, holding for 20 minutes or so seems to be the usual - whether or not the COBT has been achieved.