The Mim Time for our Ecru puzzles is an estimate of how long the puzzle takes to solve. The estimates all come from the esteemed Mim, so we could get a relatively consistent time. Of course, this is not a large sample size, so we can't guarantee that a puzzle takes you that amount of time. However, it should give you a useful estimate of length.
We will also be noting the "Normalized Mim Time," which is simply the Mim Time relative to the number of pieces. This, we think, should give a reasonable estimate for difficulty. A puzzle with 500 pieces will (almost) always take longer than a puzzle with 100 pieces, but if they have similar Normalized Mim Times, then you can expect somewhat similar amounts of challenge to finding the space for an individual piece.
These two pages will list Ecru puzzles sorted by their times as we rate them.