Never broken an ankle but have done my leg and foot. And hand. And finger.
Anyways... With the leg then yeah it was about 6 weeks off walking with it, but then I could get on a static bike before I could do anything else and I built up the fitness like that. A few weeks of that and I was running again. It was a bit hurty but you'd expect that. By the time I was back running I'd not lost too much fitness at all.
I was still in work though (office job) I did have my foot up and I'd have to go home a bit earlier but at least it was keeping me occupied.
You do get quite good on crutches anyway.
You'll be back to normal before you know it. Maybe spend some time reading up on training or something or some inspirational runners ?
Oh and if you've not watched it - catch up on Game of Thrones, Line of Duty and Spooks. That almost counts as cardio training.