It's not that there should be a 3 second timer, it's that there IS a 3 second timer.
This issue has already been exploited and patched appropriately. Plus, after those 3 seconds you need to pot, open up an inventory slot (most likely), put your prayers back on, then navigate to the special attack tab, click special attack, and click the player while also clicking outside the safe zone beforehand.
So in reality it's more like 4-5 seconds.
Additionally, ever since the spec timer update, I've never seen it bug out and not work when it was otherwise supposed to.
If you could provide footage of somebody insta-restoring spec faster than 3 seconds then that'd be something to look at.
Are you talking about double volly, volly dbow, or volly ags? Because ring of vigour makes those combos possible.