i dont mow much so blades last me a long time.
i usually say 15 hrs on the machine between sharpenings.
i know guys that put those hours in a day and a half, i go a couple weeks.
and of course that depends on terrain, grass quality, operator, ect. ect.
I got somewhere around 24 blades (stocked up some this year after reading the forum) but one mower uses 3 sets, the other uses 4, and the last set is useless gator blades... The idea WAS to only have to sharpen them once / week but the older blades are worn (due to sharpening) beyond manufacturer specs so I only run them on the older machine as it has lower rpm's, the newer machine only runs the newer blades.
Far as sharpening, again I sharpen several sets at a time then I swap worn for fresh. Swap them end of day IF 4 yards or more that day, so every day or every 4 yards, whichever comes last.