A satellite is quite unlike a thermos in the sense that it is carefully tuned to keep its temperature within a relatively narrow band around room temperature.[1] during all operational phases.
This is because, despite intended space usage, devices and parts are usually tested and qualified for temperature limits around room temperature.
[1] "Room temperature" is actually a technical term meaning 20°C (exceptions in some fields and industries confirm the rule).
Yes 20 and 25°C I believe are the two most popular choices. In many cases it makes little difference with units in Kelvin ¯\_(ツ)_/¯