Once you start, you'll be presented with a puzzle from a large collection of puzzles of approximately the same difficulty level. You won't do the same puzzle twice.
You can do up to 2 timed puzzles (of each size) each day (4 if you are a subscriber).
Players are ranked by the daily fastest time (for each size), the average of their 3 fastest times, and by the average of their 65% fastest times (Note that if you abandon a puzzle without solving it a time of 18 minutes will be stored for it).
before you do timed puzzles.