On the whole FNaF1 animatronics thing, the Phone Guy said that they're left in a "Free-roaming mode" at night, and that they're not allowed to wander during the day. So whatever the case, I assume they can't leave the stage during the day and that they may be a bit less self-aware during this time as well.
As to how this mode is activated my guess is that they were modified at some point so that they would switch modes automatically at set times. They could be heavily supervised as day approaches as well but given how they don't bother with getting more than a single guard for the night watch that seems a bit unlikely to me...