Look at it more like a guide line. Like you said, everyone reacts different. Speaking for myself, i did time on + pct = time off only for my first cycles. That and a lot of other "rules" are generic and should be adapted to each individual.
Lo, there do I see my Father..
Lo, there do I see my Mother
And my Sisters and my Brothers..
Lo, there do I see the line
Of my people back to the beginning..
Thay do bid me to take my place among them..
In the Halls of Valhalla,
Where the Brave may live forever.