Just got a Zoo Med Hygrotherm and I have some questions...

[Beebulz]

I just got a Zoo Med Hygrotherm for Christmas, and I have it set up (I think) correctly.

I just need it for the temperature. So I set the temperature I want my tank at, and it has been turning the heat lamp on/off as needed- so it seems to be working in that aspect. Although my digital thermometer in my tank keeps saying its 2 degrees hotter than the hygrotherm is saying. I'm not sure which is correct, I kind of want to trust the hygrotherm over my digital thermometer.

Another question- I set the night heat drop, but it has no time settings on there. How does it know when its night time and when to drop the temperatures?