I bought Juniper conifer in August and left it in the original pot until next Spring. I live in zone 7a and we have had a very mild fall, so my Juniper has grown almost to the point of needing to be repotted now. 
Should I wait until Spring or should I repot it now? Thanks. 

The question should be why do I want it re potted? Is it not draining well? Just because a few roots may be out of the bottom of the pot does not mean it needs re potting. Is it in a plastic pot or a ceramic pot? Either way unless there is a problem with drainage the answer is no do not do it now. If it is not draining well then there are other ways to try to correct it, push a chopstick or other spike down into the soil in a number of places to improve drainage. Scrape the top 2cm off and loosen the soil underneath and replace with fresh soil.

I second Geoff. It is amongst the top 5 questions in this forum. Beginners that think the soil a tree is sold in is bad for it an that repotting is an urgent task. But there is almost never a good reason to repot a tree in the wrong time of the year. Especially not for a beginner.