It's curious how the oil pressure decrease as the oil gets temperature. It's normal but interesting to see that the oil needs much more time than the coolant to arrive at normal temp.
Engine cold:
oil cold
Coolant cold
And, as the oil temperature arises the pressure reduces.
For me it shows how important is start and drive the first kms slowly to take car of the engine.
It needs around 5miles/ 8 kms in cold winter 6ºcelsius to arrive at normal temp.