Ok, what you asked is how long does it take to know when it's done. For me, if I take three weekly readings, and nothing changes, I'm good. That's two weeks, start to finish. If there's ANY change, or ANY doubt, wait a couple more weeks. Things can go slow. As said, don't rely on the airlock. That is not what it's for. Use your hydrometer. And always correct for temperature.
Now...
Having said that about determining when fermentation is done, that has NOTHING to do with clearing. I, too, have had meads I thought were clear develop sediment in the bottle. Very disappointing. All I can say there is it takes as much time as it takes. When it looks like a freaking crystal lighthouse lens, it's ready to bottle!