Swarm season

Swarm season runs on a strict clock, and the clock is set by the queen cell, not by you. Once a colony decides to swarm, a queen cell goes from started to sealed in about eight to nine days; miss that window and the old queen leaves with roughly half the colony before you ever see a problem coming.

A seven-day inspection cycle exists specifically to beat that clock: checking every seven days guarantees you catch any started cell before it can be sealed, no matter which day in its cycle the colony began building it.

Skipping one inspection during swarm season, or stretching the interval to ten or fourteen days because the weather was inconvenient, is enough for a colony to swarm on you between visits.