I always freeze them raw and then take out the freezer about 30 mins before I want them and then cook for an extra couple of mins. I have found they dry out a little if cooked twice, but another poster on a similar thread a week or so back said it worked fine for her.
My mum for years has made them in advacne and frozen them cooked - and then heats them up from frozen when needed - I'll check with Dad for how long. I think it is 15-20 minutes at 180C.
I also freeze them cooked but becasue I am strange and don't actually like warm mince pires, I have to defrost batches when I think I'm going to need them. I can them warm a few for dhandds guests and keep back acouple one for me t have cold
So far this year I have made 110 mince pies (the last 12 are currently baking in the oven): the first 24 for the school's winter fair, leaving some for home (and to take a few of the mini ones to the Scottish Mumsnet meet-up last night) and then another batch for the Kids Rugby today. I'll freeze 12 of the last 24 and keep 12 for dh and ds to eat this week (I'll even put one into ds' packed lunch )