When to repot Catt Seedlings?

[Kailyn]

I have three Cattelya seedlings I bought about 2 months ago. They are still very small but seem to be doing well (two of them have had a lot of visible root growth since coming home) I am a Catt newbie and really want these guys to do well. When should I consider re-potting? they are currently in the small sized terracotta pot. The one on the right has a root growing well over the edge of the pot, It's also less stable then the other two.