When does a trackstand "officially" ends (or how to measure its duration?)
(too big for a comment)...not a real answer, just a partial:

From UCI part 3:

3.2.039 The rider on the inside of the track, unless overtaken, shall lead at least at walking pace and make no manoeuvre to force his opponent through until reaching the pursuit line on the opposite side of the track. A maximum of two standstills shall be permitted for each race. The maximum period for a standstill shall be 30 seconds following which, the leading rider shall be directed by the starter to continue. If he fails to do so, the starter shall stop the race and declare the other rider the winner of the heat. In a three or four-up race, the race shall be immediately rerun as a two or three-up race, without the relegated rider.