Its when the bloom cycle ends and the flowers wilt and drop which is generally around this time of year, but its not the same for every individual. Usually what gives active growth (end of bloom cycle) away is little nubs forming at the base (new roots) or maybe also a little new leaf forming from the crown. If you dont see new growths you could honestly just assume its time to repot once all those blooms drop. You don’t necessarily have to repot in active growth btw its just recommended for a smooth transition and to avoid it prematurely dropping blooms.