I would wait till spring. Good for you though for taking the time to recondition him the right way. I agree with what others have said- just take the time to get to know him. I have done it both ways, with join-up, and with just spending time with them. I found join-up to be very good for certain horses (like one mare that was so afraid I couldn't even catch her, let alone work with her), but I also built very good relationships with my horses before I even knew of join-up by just spending time with them.
Just wanted to add that join-up shouldn't be a long, stressful ordeal either. 5 or 6 laps in either directions should do it, with Monty himself saying that it should only take 5 min or so for the average horse. It is definitely possible to do at the trot as well (I did it several times), but I don't think a walk would work. You may find that by spring you don't even need to do join-up at all because your bond will already be strong from consistent time on the ground ;)