It's not quite as simple as that if the many posts on importance of good sleep here on HN indicate anything.

Sometimes you might wake from 7.5 hours of sleep groggy and with a headache and sometimes you might feel fresh after 6 hours.

If good sleep is one of the most important things in prolonging and improving your quality of life then it would make sense to take advantage of modern technology to track it.

What's the point of investing extra $100 for retirement if you do not live to enjoy it?

Besides, I live in a country where retirement is far from certain.

I would at least like to know the optimal time for waking up.