I've been in my fair share of sus situations in my life and they've been either telegraphed (people starting with yelling, then intimidation, then getting into personal space) or ambiguous. I was recently at a block party with a loud DJ, and some guys fired several rounds and it took minutes to figure out what was going on. Even the first responders were amazingly sluggish in their response.
Hell, I had a guy sneak up behind me while I was parked in my car, bang on my window and tried to start shit with me. I had enough time to shoot off a text to my wife to stay put while defusing him.
So I personally think people with good situational awareness have plenty of time to act appropriately in a variety of common dangerous situations.