You really have no idea how much time other users spend per puzzle.
If I hit "Remove Errors", and it removes 20 errors, that costs 2400 seconds. The person may have spent less than 2 minutes on the puzzle, but it goes down as 2400+ seconds, throwing off their average!
Also, if you start a post, and don't finish it, then you can always come back to it, as long as you do it within 24 hours. You can do that with the "Recent Games" button. If I started 10 games 20 hours ago, and then finish them all right now, then they'll all be 72000 seconds, and that will greatly throw off my average.
I'm tempted to do this on purpose next month, so that it looks like I spend 30+ hours a day solving puzzles.
Personally, I'd prefer to see an average in the hall of fame that doesn't reflect penalties from removed errors and incorrect submissions. Admin, is this possible?