I injured myself at about the same point in c25k – I was climbing over a fence and landed badly! You'd think I'd know better!
I have absolutely no medical experience, so I can't give any medical guidance. What I would suggest is to talk to your doctor about it, as I'm sure they will have a good idea of how that particular injury will heal. If you have a follow up appointment booked, then I would definitely take that opportunity to ask – I would think that at that appointment, the doctor will have a good idea of how quickly you are recovering, and will be able to give you a good idea of when you'll be healed enough to start up with exercise again.
Even if you don't finish the plan, if you are mobile enough, why not do the 5k anyway? You'll get a great feel for how it is to run with other people, and you can always mix running and walking along the course (you'll probably not be the only one).
Good luck – I hope it'll go well for you!
I hope you are recovering well. I am an ER nurse practitioner, with orthopedic experience. As a general rule we instruct ankle sprain patients to use the brace until they can walk completely pain free and give the go ahead to resume athletic training when they can run full speed and change directions with absolutely no pain. Sprains can be very tricky and they require adequate healing time or you can develop "weak ankles" and be prone to chronic ankle problems.
Again, hopefully you are already up and around.
There are a few questions about injuries on the forum, and as I've not got a medical background, I can only suggest people ask their doctor, or at their gym if they have one and have a google on reputable sites. It's really valuable to have a reply from someone who actually knows what they're talking about!
Thanks again, and I hope your running is going really well too!