Probably time for you to educate an unknowledgeable here, but isn't it something to do with flow control? As flow works in 15 minute segments, and assuming (possibly wrongly) that most flights will have a 15 minute taxy time built in, then if you get airbourne before your EOBT then you are actually getting airbourne more than 15 minutes earlier than expected so should re-file the new EOBT and see if any flow should be applied. I only ask this as a few years ago I had quite a severe overload during a "free flow" period, and when the traffic count was looked at 2 entered the sector more than 15 minutes early and 7 entered more than 15 minutes late, the worst was 95 minutes late. I know that following this 2 airlines were contacted and threatened. All the aircraft were slot free due to their filed EOBT and none had updated when running early/late as they should. I do know that this has caused further overloads since but not to the severity of mine, there were other factors contributing in the later ones.