@hamster3null: timing the explosion may not be that hard.
A mobile phone, or some other computing device with wireless communication, could easily talk to another device on the ground and update/modify an agreed upon deadline until contact is lost between the device on the ground and the on-board device. The last agreed upon time would be available to the second for whoever planted the device and their friends.
Letting the devices update the deadline automatically has the advantage of not involving the planter (no suspicious activity close to the plane) and you can do it frequently right up to the point of losing connection.
As for losing connection, this would depend on whether you use cellphone connections or wireless. Wireless might be cut when the doors are closed or, for instance, a catering truck with the ground device leaves the plane. Whether this is good enough depends on how smooth things normally go at the airport (never been there, so I wouldn't know).
I guess cellphone coverage for a planted device might last until you get up to a certain altitude at least? That would let the perps update the deadline based on exact takeoff time. SMS messages would give you plenty of bandwidth for final agreements (deadline update + ack), so you don't really need wireless.
If you assume that the mobile phone can connect to on-board wifi or cellphone networks, you will have more options for factors that can update the deadline (and still keep "ground" updated):
a) pressure as measured by the phone (my old Samsung phone does this, for instance)
b) location available through on-board wifi webpages (for instance). You probably don't need working GPS as the plane might give it to you freely
c) "ground crew" can update the deadline
Programming the devices isn't that hard. You don't have be a very advanced programmer to combine multiple techniques to get whatever works best that day.
1) If you only need it to go off some time after reaching a given altitude/pressure, it's almost trivial (depending on how safe you want to be that it doesn't go off early, but you might add other safeguards than programming).
2) If you need it to go off at a known point in time that's updated to the point of losing connection, it's really not that much harder and you can just set the deadline to a point where you're fairly certain it's well up in the air.
3) If you want to let it go off when passing a certain point (to some degree of accuracy), it's not really that much harder than (2). It's just down to how accurate you need to be, assumptions on flight paths and how long you can keep updating the timer. On-board communication at altitude can add accuracy, but would be more vulnerable and might be slightly more complicated to get working reliably.
Not that I want to argue that the video is real. I just don't think timing is an argument for debunking it.