Rating level of difficulty

[azzzz]

This is what I came up with, but I'm a little uncomfortable with it. I originated it after a couple dozen puzzles (as guest) where my best time was 11:??.

I figure Stephen is automatically rating them by the time spent on them. That rating is skewed when someone is interrupted, often more than once, during a game.

I don't rate a puzzle when I have to take a break midgame because it won't agree with official time (or rating, regardless of official scale used).

I'm open to suggestions to improve this scale.

Min:Sec Rating
+ 5 minutes after first 12:30
0--12:30................. 1
12:30:01--17:30..... 2
17:30:01--22:30..... 3
22:30:01--27:30..... 4
27:20:01--32:30..... 5
32:30:01--37:30..... 6
37:30:01--42:30..... 7
42:30:01--47:30..... 8
47:30:01--52:30..... 9
Over 52:30 min......10

AND, Stephen, can stats reflect min:sec instead of seconds?

Thanks.