I actually don't think it will take that long. Re
Post# of 56323
There is a tipping point at which even some of the most skeptical folks on MJ will come to the conclusion the US policy here does not make sense on any level. If CO and some of the other states do this right, and to my knowledge there has not been very many problems with it so far, with it still polling well over 50% still in favor now that they have seen the program in action, you could see a swift change. This is shaping up to be just like alcohol. As more and more states legalize, national opinion will likely follow faster than you think.
As for the medical end of this, it should be a no brainer. If Canada is successful, that will also help tip the US polling in favor quickly. I don't think it is a matter of if, but when.