broken 5th metatarsal - walking advice

I broke my 5th metatarsal 3 1/2 weeks ago after falling in the street. Its broken about halfway down the foot, and I also tore the tendons. I was put in a non weight bearing cast and given crutches for a week. The when I went back to the fracture clinic I was given an aircast walking boot and told to use crutches if I needed them for a couple of weeks. I was told I could take the cast off for sleeping, showering or if I was sitting down for a while. The doctor said if I needed the toilet in the night I could walk through on my heel rather than putting the boot back on. I've had surprisingly little pain in it, and over the last couple of weeks all the purple bruising has gone, and the swelling is very much reduced. I can walk happily around in the aircast without crutches, even going out shopping this way feels fine. At home I've tried walking around a little without the boot on at all, and can do so barefoot. I'm starting to get movement back in my ankle which has been very stiff and I wonder how much walking I should be doing? I don't go back to the fracture clinic for another 2 weeks, and I don't want to do any further damage, but I don't want the muscles to get weak either? How much can I walk on it? I've been doing lots of exercises (writing the alphabet with my foot, trying to turn the ankle in circles in both directions, trying to grip a towel with my toes) since I had the boot and I've taken celadrin tablets since I broke it.