I've had garters for over ten years, but have never housed multiple snakes together before (due to size concerns, and my blind snake who doesn't socialize well). But it's been almost two months since Harley was officially parasite-free, and about two weeks since she shed off. I waited until she slowed down her post-illness eating frenzy to house her with anyone, but she seems to have calmed down after about two large feedings and is eating calmly now.
I'm going out tomorrow to get some decorations to furnish their joint cage, and going to get them in together within a day or two!