From my experience if don't act like your doing someting wrong nobody will think your doing anything wrong. I smoke in my front yard, back yard, garage, ect. day or night and have never had a problem with any of my neighbors. Just be a good neighbor to every body and don't make it look to obvious. From 30-40 feet a joint looks like a cigerette and if your nieghbor starts walking over to visit with you just put it out like you would a cigerette.
I don't know if my neighbors somke grass or not nor do I care to find out, that's just asking for trouble if you ask me. These are just my experiences and may not be good for you but from what I have seen most people don't give a shit what you smoke as long as you don't do it around their kids or something stupid like that, shit I've even smoked with a mass. state trooper and it was his joint. In short mind your own buisness and most people won't fuck with you.
peace, redeyed