The number of laps you need on a finishing Ark, like a Hard Black or Translucent, depend on the preparation of the bevel up to that point and the prep on the finish stone. Burnished stones are slower, but finer cutting.
If you are doing full Ark progression, you will need to do more finish laps, depending on how many you did on the middle stone, the transition stone.
The first stone the bevel setter, shapes the bevels and leaves deep stria. The middle stone, begins the polishing process, removing the deep stria and straightening the edge, (transitioning from shaping to polishing). The finish stone removes the middle stones stria and straightens the edge further, for a silky smooth shaving edge. If you leave deep stria on the bevel, you will have a chippy edge.
Now days, I use an Ark, to finish after a 12K or even a 20kGS. So, the edge is very finished/polished and probably going backwards in grit. The number of laps needed is not as many, because the only stria on the bevel is 12 or 20k. The finished bevel shows no stria and is a hazy (Kazumi) bevel and the edge laser straight and chip free.
The number of laps depends on what the edge needs and what was done up to that point. Just look at it. The bevels could feel smooth on the stone and the edge can still be chippy, depending on what was done in the progression.
Micro bevels work very well with hard Arks also, because of the slow cutting of a burnished stone. Just finish on a synthetic up to 8 or 12k, then add a layer of tape and do 5-10 laps on the finishing Ark. You should have a very narrow secondary bevel and a keen smooth edge.