A short while ago VUCs Randulo tweeted that he had recently updated the firmware on his Polycom phones. He said that he did this using a local provisioning server setup temporarily just for the task. If you’re using a hosted IP-PBX then you may not have a suitable server running 24/7/365.
If you don’t run a provisioning server all the time then booting the phones can take a lot longer. On boot-up the phones simply fail to contact the provisioning server and eventually boot using their existing internal settings. But this means waiting through a series of time-outs, which is the principle source of delay.