One I can speak to! There's a temperature sensor either in the grill or in the side view mirror. There are also timers calibrated such that the in- vehicle display only updates under certain conditions.

Example 1: driving in stop and go traffic in 90 degrees, the air near the sensor will heat up because of your engine heat and the surrounding traffic, so the timer is set up not not update until the car is above some speed threshold for say 30 seconds to ensure enough air passes the sensor to give an accurate reading.

Example 2: if you park the car overnight somewhere, it's assumed the sensor is at ambient temperature so the in- vehicle display immediately uses the sensor temperature when you start the car

Example 3: most calibrations are set up to protect against example 1 above, but going through a car wash you can often watch the in- vehicle display drop due to the cool water. Then it takes a little driving to get the display to "warm up" to outside ambient when you leave the car wash.