I've heard that 6 months rule too: once you feel back to normal, you stay on meds for another 6 months. The docs call it 'maintenance'. But that's an ideal thing not a must do. When I was on meds before having baby I was about 2 months into the 'maintenance' period when I got pregnant so I just started weaning off then, though when we try for #2 I want to be off them before getting pregnant because with all the hormones that fly around your body during pregnancy I find it hard to tell what's leftover depression or whats fairly 'normal' for pregnancy.
The best thing you can do when coming off meds is to do is super-slow. This decreases the chance or relapse or of withdrawal effects. The higher your dose or the longer you've been on it, the slower you should take it . Xmas is 5 months away, which is lots of time
I don't really know how to tell when you're ready to come off. I think when you have been feeling normal/healthy/stable for awhile. I am in the process of cutting down one of my meds at the moment and when I decide when I'm ready for cutting down to the next level I do it when I have thought "I'm ready!" for at least 3 weeks- that way I know I'm really ready.
I think there might always be a bit of a risk but if you wean slowly, carefully and are still looking after yourself in all the other ways that can help, then you've got a good chance of succeeding :-)