Yes, they're currently sorted by best time. I was thinking of incorporating the other values (tools left and lemmings saved) but wasn't sure of the best way to implement it.
The generally accepted hierarchy is to
rank by lems saved first;
if equal, rank by skills used;
if equal, rank by time used;
if equal, rank by whoever achieved the record first.
Sometimes, there is analysis on how to complete levels faster or with less skills at cost of less lems saved, but this is more seldom.
-- Simon