According to Robinson, you
have about 1.1 seconds to lower the collective and enter the
autorotation once the engine dies.

Thanks for the reply. It is very helpful. But I am astounded that the
emergency handling window is only 1.1 second. According to AOPA, pilot
usually takes 3 to 4 seconds to "register" the emergency before s/he
react. 1.1 seconds is out of AOPA's range but it is on the edge of my
standard. I had chance to let my Piper running out of one tank. That
probably took me 1 second to switch tank. The second day, engine
stopped again inexpertly in the cruise because there was air bubble
went into the fuel line, that took me about 1 second to turn on the
fuel pump. But it does on edge if R22 is only 1.1 second. You have
absolutely no window for the mistake, second guess or register the
problem slowly.