A protective cap that screws onto a tank valve. This keeps the valve from being damaged while not in use. I highly recommend this. This means someone is trying to push on the cocking pin on an autococker to make it fire faster. The beaver-tail stops this from happening.
Timing is a autococker term.
If a cocker is not timed right it will not function properly. Timing should not be attempted by a beginner. This feature comes on some markers like the shocker. When turbo mode is on you get 1.5 shots for every 1 trigger pull. This is similar to full auto, but not quite as fast.