During the boss fight at the end of the game(where the giant girl tries to break through the barrier by repeatedly hitting it, and you're on a timer counting down), you must do the five challenges rather quickly!
I found that as long as I didn't fail on any of the five challenges, I didn't have to rush too much.
I don't know the exact time, but I think as long as you have more than 30 seconds left you'll get the achievement. (I had 34 seconds left. I've seen someone else mention they got it at 31 seconds.)
Also, there's no easy restart of the boss fight. I found the best thing was to just let the timer run out, as that at least sets you back to the beginning of the boss fight level. (Exiting and continuing will have you all the way back at entering the monorail, picking up the gun, doing the bell puzzles and axe + electricity challenge, and watching the long cutscene all over again! So just let the timer run out instead, much easier.)