If I remember correctly, the offsets were measured in words (16 bits on the M68k), and then you had scroll registers where you could offset with 0-15 pixels.

This was complicated a bit since you only had two scroll registers, one for even and one for odd bitplanes.

No idea how this was implemented in hardware.

Not particularly. Think of the display as a "stack" of monochrome one-bit-per-pixel images. Then bit offsets become completely natural.

I was thinking in terms of word alignment and synchronisation issues.