I can't imagine a group in which all the players are "lawful" enough to accept the use of a timer. The old "you should have enough time to decide what to do while you're waiting" just doesn't work with a lot of people. Explaining that your character is also in a high pressure situation with only seconds to decide what to do also doesn't work.
Unless you're with a group of people that all have the same mindset, combat is going to take a long ol' time.
Unless you're with a group of people that all have the same mindset, combat is going to take a long ol' time.