How can V-USB work with a controller frequency of 12 MHz?

Question

Arduino

I became interested in the topic of the USB bus, and is it possible to implement software support on the atmega328 microcontroller.

I came across the V-USB library, and the requirements indicate that it works even at a frequency of 12 MHz, though in low-speed mode. But anyway, how is it possible?

After all, low-speed offers transmission at a speed of 1.5 Mbps -> 1572864 Bps. So one bit is transmitted somewhere in the course of 0.6357 ... microseconds.

Meanwhile, with a controller frequency of 12 MHz, the time of one cycle is approximately 0.083 microseconds. That is, approximately 8 cycles for the transmission / reception of one bit? Sounds like insufficient conditions, even entering an interrupt takes a few cycles.

Am I doing something wrong, or am I fundamentally wrong about everything?