From 104 to 92? When checking with the OBD scanner it is like 15/20 seconds maybe. Maybe 30? Haven't really measured it. But it is quite fast. Seems to me like the thermostat is "sticking" or something.

 

Cheers everyone, today I was doing some more work (sway bar bushings etc.) so was crawling down there at the front and notice some red fluid on the power steering cooler pipe.
Did a quick "taste" check and checked the direction it was coming from - bingo, the radiator has a leak that will be causing these temperature fluctuations due to pressure changes I think.
Ordered a new one. Luckily I haven't started replacing the thermostat so I have the fresh coolant left and can do a complete change.