Lets say you buy from a dispensery and keep it in the medical cylinder you got it in at room temperature away from sunlight. How long before it starts to lose its potency in the slightest?
What makes you think that. It not growing anything but mold... I really depends but id keep in the frige if i were you. Lasts longer. If you go for the freezer it will dry out faster but will still stay potent. you will just be smoking powder when you grind it. Really it depends on how dry it all ready is. Ive had weed that turned to powered or mold in 3 week and weed that lasted months and everything in between.
If it's not wet as fuck, and it's in an airtight container, why would it get moldy? I've kept weed in a Mason jar for about 18 months. When I took it out it was as sweet as any bud I can ever remember ever.
if it's in a cool dark place, many years. it will not be pleasant, but I've gotten high off two year old weed that was kept in a sack.
depends how long the dispencery had it B4 you came along my way is basement ive had mine 3 years fresh as harvest day