When used here, the purpose of the ! depends on whether they want to have the input be now or when the timer executes.

You can see the difference in these example. Both of them echo the string to the active window, but the 1st asks for the input right now before launching the timer containing your literal password, while the 2nd one launches the timer now and then waits 4 seconds to ask for the input. Note how there's a different result if your password is the length 8 string $version or is a word beginning with %

Code
//timerQuotePass 1 4 echo -a .quote PASS  $$?*"Password*:" | timerquotepass
//timerQuotePass 1 4 echo -a .quote PASS $$!?*"Password*:" | timerquotepass