Honing is a progressive process that goes from the more coarse to the more fine. You're right that it will take a longer time to hone a dull razor on an 8k norton waterstone than it would if you started on the 4k side and then went to the 8k and then stropped with leather. When you've started to get consistent results with the 8k, move on to a coticule, escher, or thuringian and you'll see a big difference.