The original question was about the minimum password (or PIN) length (or entropy) for the screen lock in Android. Seeing that nobody answered, and following Schroeder's advice, I'm going to edit it and just focus on the speed of the unlocking process.
So say you are an attacker and you find or stole an Android device, it's turned on, but it's locked by a password (or a PIN). What are the most common and feasible ways to unlock it or access its contents anyway, and how long would that take? Note that I said "feasible ways", because I'm talking about a real average-skilled attacker, not about government agencies or theoretical attacks that nobody in this community would actually be able to do.