I am no woman, rather a teenage boy. I have never smoked pot, but I have many friends who do it regularly. I know how people get when they are high, and it can be inconvenient.
Try your hardest to get him to quit it all together, and if he will not comply, I suppose the best you can do is to allow him to do it perhaps early in the day before he starts at his work.
If it impairs into his time, then tough for him. If he chooses to smoke pot, it should be at his own expense, not at the expense of his wife for 17 years who is fighting through cancer.