Here's the logic designed into the system. Maybe this will help.
I've seen this when there is a lot of condensation and/or a trip through the car wash. The sensor gets cooled and insulated by the water that doesn't disperse right away (although your time frames seem extra long)...It's 95 degrees out and the outside temp sensor says 54 when RL started up middle of day. After about 1 hour of driving the display slowly rises to proper temp. It never took this long before and would show accurate temp reading when first started up. I could have bumped the front bumper on large dirt clods on the job. Nothing appears broken. Typ. scenario.. go to work 6am temp says 64 outside which is about right, get to job day gets into the 90's, RL has been sitting for maybe an hour in sun I start it up and temp says 54 and stays 54 untill i drive home home(about an hour drive) and the temp says up in the 90's as it should. Sound familiar to anyone?