Once they got my prescription right it didn't take me any time at all - I can barely see the marker between the three different bands on my varifocals. I have a wide bit at the bottom for desk work and reading, a fairly narrow medium bit in the middle which is set to the distance between my specs and my computer screen, and a wide bit at the top of distance.
The opticians made 4 sets of lenses for me before they got the balance just right. They need to take the stance of your head into consideration too - I raise my chin a little normally, so it's no good testing the lenses reading a book or sitting in the chair, I have to stand up so I am standing "normally for me" to test if the lenses are set up right for me.
It's how they have merged the various distance lenses which can make it difficult. Once they got mine right, I don't even notice that there are differences in the separate parts of the lenses.