I mean that's not terribly late. And there's always control wards for vision which you should be buying on every back if possible anyway. It's entirely situational. If I need some gold and I can cs without fucking up a freeze I will take the farm. If I'm 200 gold on support item as frostfang user at 12 minutes I won't set myself too behind by taking farm but I'll take around 3-4 minions but thin it out otherwise. I'm not sure about how long the timer is but take as many as you can where when you come back to lane the timer is reset. Don't clear 2 wave of minions if you're really behind on support item but do it if you can complete a valuable item (boots, component item etc). Again it's situational and you should be at the point of the game(in terms of skill) where you can decide what's better for you