Generally a MAC address is learend as soon as a valid frame is received on a switchport. The source-MAC-address then is stored in the MAC-address table of that VLAN with the port it was received on. Now the switch can forward unicast traffic to that MAC-address as destination. If no more frames with that MAC as source are received, the entry in the MAC-address-table will be deleted after 5 minutes by default. If the switch now has to forward a frame to that destination, the frames have to be flodded over all the switchports until the entry is re-learned.
As stated in the posting above, you should configure edge-ports with spanning-tree portfast to speed up the learning-process when the interface initializes.
HTH
Rolf
