I remember reading an actual scientific report that 1 hour in a sealed room enriches the co2 to optimum levels for x amount of time, not sure of the exact figures but I remember that it was definitely beneficial and did absolutely no harm.
I wondered if bringing a few dumbbells in there and knocking out a few reps would increase my respiration which would increase the effect, but found it is much easier to carry a 20lb co2 cylinder up the stairs 1 time every 3 weeks rather than doing weights every day.
Time spent with your plants is time well spent though, I talk to my girls every single day and tell them how beautiful they are, that I'm proud of them, and that they make me happy. I'll second what tip top says though, hanging out with the plants is fine but if it's in your nature to obsess over every brown spot on a leaf or every 1/1000th of a shade off optimal green and then try to diagnose and immediately treat it, then don't do it...both for your mental health and the plant's actual health.
Also, I'd toke up before you go into the room, not while you're in there. There's nothing additional in smoke that helps.