mine always takes a few seconds to begin ramping up to the speed the blower has been set at. Normally I would switch off the blower when I pull up for the evening, occasionally I would forget. So when I start the car the next day, after a few seconds I will realise the blower is ramping up to speed (normally switch it off then).
From that I noticed that when the engine is cold, the blower would take very slightly longer than it would if I had been driving. It doesnt start to ramp up until I have reversed out of my parking space. I have always assumed it was to do with the extra strain on the engine when cold. Cold oil plus the compressor running would create a little extra drag on the engine for those critical seconds to get the oil around it.
Take a note of it when the engine is cold, and when warm to see if there are variations. On mine there is, but it is small (1-5 seconds maybe), but then temps for me rarely get below freezing (and even rarer to get about 20
)
When the engine is warm and the ATC is set to auto, as mentioned it also takes in ambient temps when begins to ramp up the speed of the blower.
The gradual ramping of the blower on start up also makes it a little more pleasant compared to the shock of a instantly blaring blower
