Hi,
It depends most of the STP protocol you have running; BPDUs packets are sent in different times (for example, RSTP is faster than STP because it has only 3 states). According to this, switches sent BPDU packets in a certain time. When hosts discover another switch with best priority, STP run again in order to re-converged the network and elect news root, designated and block ports
I hope it could explain, if not, maybe I could do a little topology.
Best regards.
-Eduardo