Question about a dehumidifier

I bought a dehumidifier a couple of weeks ago. It’s been great. If I have laundry hanging up, I turn the dial on full, and let the dehumidifier stay on all the time, helping my laundry to dry, and I can see the trough fill up with lots of water (about 2 liters or more). When I’m not using it for the purpose of helping to dry laundry, I turn the dial about 25%, which means that the dehumidifier comes on for about 10 minutes, then switches off for about 20 minutes, then comes on again, etc. On this time switch thing, when I come home, I can see how much water it’s sucked up in a day (maybe just 1 liter or less.)
However, recently, I turned the dial to 25% and went out all day. When I returned, I saw that barely any water had been sucked up! Does this mean that the time switch is broken? Or that there was less humidity in the air? Ie, How do I know whether the machine is set with a time-switch, or a humidity detector?

Buy a thermometer/humidity combo … it’s cheap and you can see how high humidity is in the house and accordingly operate the dehumidifier … at the moment in our house it’s only 31% humidity, so no use to have a dehumidifier working, even at 25% capacity.

Yes, Taiwan has days with really low humidity!

So, could I assume that my dehumidifier runs according to a humidity detector, rather according to a set time-switch?