I have a Nest Temperature Sensor and it takes a considerably long time to adjust to a new temperature. Just to check, I placed it near my thermostat to get them reading the same. They started out 3 degrees different and it took 20 minutes for the sensor to read the same as the thermostat despite being 2 feet away.
Once they aligned, I took the sensor outside where it was 20 degrees cooler. After 20 minutes, the sensor read only 8 degrees lower than it did inside. At this point I took it back inside next to the the thermostat and after 30 minutes, it still read 3 degrees less.
Because the sensor is so slow to respond, whatever room it is "controlling" gets considerably hotter than desired since the sensor takes so long to register temperature, then considerably cooler than desired because of the same issue.
How do I adjust the sensor to read the temperature of its environment immediately?
It's due to the poor design of the remote sensor. The plastic housing it is contained in doesn't have any openings to allow ambient air to circulate into it. In order for the remote sensor to read the temperature around it: 1) the plastic housing needs to heat up, 2) the air inside the plastic housing needs to heat up, 3) the sensor needs to heat up to the air around it (inside the housing)
This will always mean the reading will severely lag behind ambient condition if you are actively heating/cooling. As the room heats up, it will always read a little cooler and then the actual temp. When the air reaches the high temperature you want, it will still be reading cooler and keep your heater on longer (making your room warmer than you want). When the room cools down again and it's time for the heater to kick back in, it will still think the room is warm and won't kick the heater on until after you are well below.
When you are cooling a room down, the same thing will happen. It will kick on your AC at a hotter temperature and later than needed. Then run longer and to a cooler temperature.
The only way to improve or fix this is likely to add holes to the housing near where the sensor is located. But I'm not about to waste $40 to try something that might not work, could destroy the sensor, and void the warranty.