When they are comfortable and you don't have any "hot spots" to address or deal with (blisters, rubbing, or just pressure like on ankle bones or bunions that can be fixed by having the boots punched) and you aren't fighting the boot to get the ankle to bend enough, or feeling like you "can't" bend as much as you'd like to... then they are broken in. I like to describe it as the moment where they no longer feel like "new" skates and feel like "your" skates
Boots can be 'broken in' by some skaters in just a few sessions, or it might take months - it just depends on your skates, what kind of skating you do, how much you skate, and how sensitive your feet are. It's not something that someone else can look at and tell you - you have to decide.