Jhin ULT Bug

Can you take a look at Jhin's ultimate? I just played my first game with him and I don't think the cooldown reduction (10% for every shot unused) is working properly. I was using his ult in the game and the cooldown time regularly was 108 seconds and I used the ult and when I finished the cooldown was 124 seconds (maybe I was seeing things). ANYWAY, I used it again in my base and didn't fire a single shot and the cooldown time was STILL 108 seconds. If the math is right, not using a shot would be a 40% cooldown reduction so around 65 seconds it should of been but it still took the full time and no time was reduced. Is it working right or is there only a specific way it can be used for the cooldown reduction to work properly?