From the UCI track cycling rulebook for the 200m sprint. Standstills used to go for many, many minutes until this change......


Sprint
The rider on the inside of the track, unless overtaken, shall lead 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.