It's the time it took the player to move.
It's so you can easily see which moves the players spent the most time on.
If the longest move was 1 minute, then all the bars will be adjusted accordingly. A move taking 30 seconds would only be half as long. But then if a player takes 5 minutes on a move, all those bars will shrink and the 5 minute move will be the biggest. Maybe that's what you mean by they don't seem consistent.
they don't seem consistent