I couldn't find any reference to this anywhere, and while it's not a huge thing, it seemed kind of interesting so I figured I'd share it with the BST purists. I was working on a system to display remaining charges based on the client data without relying on gear tracking, and observed that the client displays timers by using a negative offset value for your reductions.
So, the base timer is 90 seconds. If you have merits and charmer's merlin, the offset is -45 (-15 seconds each, x3 charges). Your remaining charges are displayed with:
floor((90 - offset) / 3)
and your time until next charge is:
floor((90 - offset) % 3)
Now, what's interesting is that the server seems to obey the same logic, but recast timers *don't* always update the offset. So, for example, you can do this at the end of an unleash to get an extra ws in:
-Ready with -5 gear and JP 4x, leaving timer at 30 seconds(last one will have a short wait).
-Ready without your -5 piece for a 5th. The client will say you don't have a charge, but because your offset changed from -60 to -45, the server is calculating your next charge as requiring 30s or less on recast, which you have.
Note that this will cost 15 seconds on the last charge, pushing your recast to 40+ and making you wait until it hits 20 to do another ready with your -5 piece. I don't think it's hugely useful or game breaking, might be slightly neat for a zerg, but overall just a fun bit of trivia I thought some people might enjoy.