I got back on mine after 6 weeks but doctor recommended 8 - I only went for walking hacks tho! You will find your arm gets tired quickly. The physio told me "You're fine to ride so long as you don't fall off." Took 2 months before I was ready to canter/jump a TEENY bit but I probably shouldn't have!!
I would recommend you get someone else to handle your horse for you for a while too, mine turned into a complete MONSTER when he learned how weak I was!!!
However on the plus side, if you dislocated it at the same time your elbow will be stuck in a bent position for several months which is fine for riding, but not suitable for several other sports, so you can look on the bright side there
Chin up, it's a bugger but it will get better. Make sure you get plenty of time on the sick and watch Jeremy Kyle - hilarious!