Night and Day
Precisely, to "prove" a hot spot you have to prove it is warmer during both day and night, and that neither is a coincidence of geometry - like a rock spire that soaks heat up most of the day but just happens to be in shadow when you take the IR daytime shot.
Those Hellas spots of mine are 20-40K warmer than ambient during both day and night, even though "ambient" changes.