The best way to notice is when the plant material is no longer losing weight -- preferably it loses a few percent of moisture in cure. You never want it bone-dry, of course. Think what results at room temp with 58-62% RH is 7-8% of mass moisture content? Doesn't matter exactly what it is because we aren't using lab equipment to measure. It'll reach that targeted 'equilibrium' moisture content in cure with the proper temps and RH%.
2-way humidi paks make this much easier and give room for error when you do put them in a sealed container. Do not go cheap. Boveda work well. Integra boost humidi paks work like shit. I've kept a temp.rh probe in my storage buckets for multiple months. Boveda are +/- 1 RH, though the probe is admittedly +/-3%. Integra never kept them moist. I threw them out after a couple years of trying to use the cheaper option.... Integra Boost is trash.
Anyway, until i got a very consistent drying process down and enough familiarity to adjust to different density of nugs, I used to weigh a few tester nugs of different sizes - tag or place in specific spots so you know which to weight as it dries. Once it stops losing weight, you know it's at equilibrium with the environemnt -- as i said above, you want the last little bit to gas off in cure. Ensures you don't over-dry. You'll get familiar with the weight of the nugs and the 'feel' of the nugs exterior.. you can learn to feel when they are close but not quite there.
If you seal it up and they get soft / moist again, you remove them for more drying. Good to spot check after 4-8 hours or so... see how they react to a sealed container. Verify that you dried them enough to avoid growing weird shit in your containers.
Maintinaing a consistent temperature and RH% will give you a proper drying length, too. The more consistent you are with this, the more predictable everything becomes.
In addition to controlling enviornment you can wet or dry trim or leaves buds on branches or cut them into individual buds to dry to further impact how long it takes to dry... e.g. if you know it's going be a bit warmer or maybe a bit dry, you hang entire plants to delay drying times.
pointn of reference.. In winter, i have a bedroom i use that is 68-70F. I used a humidifier to maintain 60% (58-60%). I wet trim and cut down to individual buds. It takes 9-10 days depending on density of buds. this is incredibly consistent because i keep the environment consistent. humidifiers are cheap... controlling temperature is not cheap. A big reason in grow in the winter.
So with those temps/rh, if i left them on branches or hung entire plants, i'd expect maybe 12-14 days drying. If you have temp and rh spot on, you also can't over-dry, or at least it'd be incredibly difficult to do so. Can still ose excess terps to enviornment, but you won't get dry, brittle nonsense. When at equilibrium with enviornment as much moisture is condensing on the buds as gassing off - which is why the mass will remain constant at that point.