Average lifespan of a chain varies incredibly. Skinny vs. Fat rider, hilly terrain vs flat, 200 miles through dirt and silt vs 200 miles of clean running. I'd hesitate there's no singular answer to that question, just what's average for
you.
That video is slightly inaccurate for our bikes in the measurement but the rest is fine. They use a 5xx chain on the FZ6, while ours uses a 428 chain, and the pitch (pin-to-pin) is different. On our bikes, 12 links is 12", so you can use
the Sheldon Brown method and estimations, as bicycle chains are generally roughly the same spec - 12 pins, 12" is spec, or 10 pins and 254mm.
12" method:
1/16" stretch = approx 0.5% stretch. Worn, still good to replace without doing sprockets.
1/8" stretch = approx 1% stretch. Chain is worn out.
10 pins, 254mm method:
1mm = 0.4% stretch, chain is worn but good without doing sprockets.
2.5mm = 1% stretch, chain is at manufacturer spec limit.