Used stone works well for carbon knives
I have the regular Shapton Glass 4000 and this HC one. The HC one feels a bit harder than the regular one. So it requires less lapping than the regular one. I used the 4000 to thinner the blade and the 8000 to finish the edge on my Aogami Blue Super/White knives.
I used to sharpen my knives only when I felt they were dull. It took me around 45 minutes and stepping from 500 grits to 1000/2000 grits and finished with 6000/8000/12000 grits depending on the knives. The hard high carbon steel knives were easier to sharpen than the softer ones but definitely takes a longer time.
Using the combination of these two stones for less than 10 minutes every few weeks (depends on how often you use your knives) should be able to keep the knives on factory performance all the time.