Absolutely not. It would be like drinking alcohol during break times because it can interfer with an employees performance. Most place of employment will certainly fire someone for that.
WHAT DO YOU THINK? MY GOD.......If you are stupid enough to ask this, I think you have already been smoking on the job. IT IS ILLEGAL and against ALL COMPANIES Policies..If it IS legal in your state, you are only allowed to smoke it in your home or backyard, not in public.....ANYWHERE!
Ultimately, this is going to come down to individual workplace policy. Generally, weed, alcohol and other drugs are not considered appropriate in most workplace environments.