I activate all skills multiple times per day, but the achievement progress only seem to increase tens, at most a few hundreds of minutes per day.

What skills are involved in the achievement? Should all nitro related skills be activated together?

The max is 7.8k, let's round that up to 8k.
8000 / 60 = 133.3 hours
133.3 / 24 = 5.5 days.

I have been playing for months now! (4k+ hours!). I should have gotten this achievement 10x by now, easily.