When a domain expires, how long before it is able to be purchased? If it is Registrar Locked, does that have an effect on the possibility of an immediate sale?
Typically 45 or so days from expiration. It will go into a redemption period for 30 days, then a pending delete status for 6 days. Once it's in redemption period, you can predict the exact day it will be available.
its actually 60 days, a 30 day grace period is given, then 30 days for the host to aquire it for themselves, after that its anyones.