To my knowledge there is no 3 second limit is there?
It is my understand that what Divine Execution does is it removes the: "Only applies after successful Jab, Kick and Punch"-requirement, and enables you to use any 3 hostile abilities to proc it. With Global Cooldown it does end up being just about 3 sec though.
Whether that was intended or not is another question
Regardless, it could certainly use a buff and make Combination proc off every 1 hostile ability instead of taking 3 hostile abilities.