When you hear advice from “successful people,” take it with a grain of salt before you do it. Look at the context too.
When they say, they sleep at 9pm and wake up at 5am. Are they referring to their NOW or was it like that even at the time they’re building up their road to success? Did they not spend sleepless nights too to reach the point of enjoying 8 hours of sleep every night?
It’s not a “one size fits all” formula all the time. What works for them might not work for you, and what’s effective for you, might not work well for others.
Success is personal and subjective.