if a monster has a bleed token (including a named monster) when does the OL resolve it? at a) the start of his turn or b) when the monster is activated, if b) could the monster be left unactivated and therefore not have to resolve the bleed token?

Bleed tokens (as well as all other effects on monsters) are resolved when the monster is activated before the monster can take any actions. Each monster must be activated on each of the overlords turns even if they do nothing and stand still.