Well, I would say I smoke once a month. Maybe twice a month if needed. So 100mg a month. Almost a year. That is, if I do not share.
Not long, cause I tend to share quite a bit also. If it were in the summer during festivals, 3 hours. I would have a DMT smoking circle, handing around my peace pipe.
First time I had more than a gram it lasted me about a week. Got five friends to breakthrough and smoked myself insane. Good times...