Most of them never passed an hour, despite the time to actually finished the game on Normal would be at least Triple that.
A run of the game only takes ~20-25 minutes, somewhere between that range. I'll be generous and say 25 minutes.
If you're replaying the game on different difficulties, characters, or delving into practice/spells, then yes the playtime would be higher, but I wouldn't expect most people to play the game for more than a few hours at most. Besides, as Drake mentioned, most people of that category have already played the game before, regardless of the means. There's a portion of people who bought the game just as a means of "support", since means to do so is pretty difficult before this, so those people are also included in the <1 hour club.
Personally I just got my lunatic 1cc and left, ages ago. I did also play around with the game a bit, tweaking with mods and game files and stuff, but otherwise I'd say I didn't spend much time on this game at all. Compare to people like Yatsuzume who took the time to get LNNN, or a bunch of friends who focused on scoring extra or other difficulties, which definitely clocks up quite a bit of hours.