Here at the good old College of Knowledge in the UK it has been taught that, for the purposes of ATC recording the arrival or departure time of an aircraft, the next minute starts at 30 seconds past the minute.......I'm sorry, I'll read that again. If the time is 17:54 and 28 seconds when the aircraft departed then it departed at 17:54. If the time is 17:54 and 30 seconds (or 30 through 59 seconds) then it departed at 17:55. Etc, etc, etc.
I can remember being taught that on my Cadet Initial course (that dates me) by one Doug Shoulder (that dates me even more), but the question is:
where is it laid down? What is the reference?
The UK AIP GEN section says that times should be recorded "to the nearest minute", as does the Saudi AIP. But where does it say that the 30 second mark is the changeover point? And is it a world-wide convention or peculiar to the UK (and possibly Saudi Arabia)?
Where's ORAC?
Perhaps this should be in Jetblast.