In game, when you play the whistle, all action is frozen for about 3 seconds, and secrets triggered immediately after. How about making it so that under item properties, you can change the amount of time everything freezes? In my quest, I made the whistle the OoT and the only song it can play (until an ocarina is implemented) is "The Song of Time." The song lasts about 10 seconds and it's annoying that when it 3 seconds pass, the song continues, and everything is moving again.
So in short:
Under Item Properties, set the amount of time everything freezes when the whistle is played, which would also determine how long it takes for secrets to be triggered.
Plausible for before 2.5?