i think the idea isn't to sleep late and wake up early consistently. instead it's about waking up at the exact same time everyday, no matter how late you went to bed the previous night for reasons inside/outside your control. the expectation is that the next night you'll feel sleepy earlier and catch up.

in contrast, walking up late one day because you slept late the previous night will wreak havoc.

I'm only trying to clarify this because it works the same way for me.