Timing our sleep time

Being a typical salary earner, we often struggle with time.
In short, not enough time (and also money). Well, this time i read some interesting stuff about timing our sleep and let's zoom into the latter which is less complicated.

This came from my favourite site, lifehacker, which apparently, is a compilation or contributions from various blogs/sites.

The typical duration we should target for is 7.5 hours a day.
We start at let's say 11.30 pm and time if we do wake up after 7.5 hours. Do this for 3 days and see if we wake up before our alarm.
If we don't then move this for 15 min and observe for another 3 days.
When you reach the point where you wake up right before the alarm,thats the sleep duration that your body really need.

Interesting idea. But what if we do heavy physical activities daily? Or on intervals such as gym? Or we have a very emotional state? Been through a stressful ordeal?

The list seems endless..well, you get the gist of it, don't you.
Nevertheless, this is still a good idea to try since with good health through getting the right amount of sleep you body need, you spend less on medication in the long run.
Good health + spend less $$ makes a happier guy/gal

That's what i think about it anyway.
At the end of this post, it seems like i raised more questions about this topic than original idea of clarifying it lol.