Very interesting. I'm intrigued to know if anybody with experience knows why there is a common recommendation of warming the mineral oil, versus room temperature which the author did.
My guess would be that in addition to the viscosity, it preemptively compensates for the thermal expansion of the oil, since on your wrist will likely be warmer than room temperature.
Here is another detailed liquid-filled watch guide [0], which talks more about handling thermal expansion, where rather than using an air bubble, he opts for some sort of foam ring. Another person recommends Flourinert with foam rather than mineral oil [1].
To be precise, warming makes the oil exponentially less viscous, so it can be a really pronounced effect by warming it 30 degrees (depending on the specific oil).
Here is another detailed liquid-filled watch guide [0], which talks more about handling thermal expansion, where rather than using an air bubble, he opts for some sort of foam ring. Another person recommends Flourinert with foam rather than mineral oil [1].
[0]: https://www.christopherwardforum.com/viewtopic.php?f=5&t=496...
[1]: https://forums.watchuseek.com/f21/liquid-filled-citizen-6540...