Not precisely. The best time to try is right after everybody has been moved to the last flight that departs before your flight to the same city. For SAN-OAK, that might be 1 to 2 hours before your flight time, so probably at the gate. For MCI-MCO, it might be 3 to 4 hours, so probably online.
Good point. So if PAX A is on my flight with an A18 BP, but changes to a flight departing 2 hr. earlier (by paying upgrade or has full fare tix), then his number becomes available at the time they move him from my flight to the earlier flight. Right? As that likely could happen between 2hr 15 min to 3hr. 15 min before my flight departs - that would be a good time to have someone cancel my BP (from home on line as I often have no PC access at those times) and then "re checkin" for new BP. So that may be the sweet spot for that flight.
Can one cancel and re-check in over and over on line, trying to time it just after a BP sequence # is released? I have never done this.