It usually takes about 6 weeks for bone to reform enough to begin putting weight through it.
Then, you'll probably be in a walking cast, to allow enough weight to go through the bones to help the remaining parts to calcify along the stress lines (points through which normal stress of weight-bearing cause thickening/more bone placement during growth).
I'm so sorry for your injuries, and the associated pain. I'm glad you're alive though--how'd you break both legs??? OUCH!!!
You're going to need a good physiotherapist when those casts come off...feel free to come to the states...I'll be graduating just in time to take care of you!!! 😀 😉 😛
Good luck!!!