No. You can only reduce a timeline to the point where it cant be effectively reached. A timeline that is guaranteed to be missed is no longer a timeline. It's an arbitrary point in time with no real meaning in relation to the work at hand.
I get the point you're trying to make, but in the fictitious scenario you're making, if everything, I mean absolutely everything, is done in 4 days and you're just spending the 5th doing nothing, this isn't Parkinson's law at play, this is just inefficiency.
The idea that something that could be done in 5 could also be done in 4 is less about 'wasting time', but about 'aggressive prioritisation' (which may or may not involve corner cutting).
And even in the case where there is no corner cutting, I think it's a mistake to think that the work going into prioritisation has no cost or overhead, or that this is scalable for months to come.
At a personal level, I find that if I push myself to finish something "more efficiently" because of a deadline (most of which are typically arbitrary rather than organic), this has a backlash effect on my ability to do things efficiently in the projects after. I would imagine a similar risk exists at the organizational level.
> but in the fictitious scenario you're making, if everything, I mean absolutely everything, is done in 4 days and you're just spending the 5th doing nothing, this isn't Parkinson's law at play, this is just inefficiency.
"Absolutely everything" can never be done, because you have things like unknown unknowns. Things that reveal themselves further on in the project and are almost impossible to anticipate.
Alternatively, things like "improving documentation" can also be done nearly in perpetuity. There are always more use cases, caveats and scenarios to describe or examples or onboarding materials to refine for future newcomers.
These are the less-critical things that should be done on a Friday at the pace of the person who is performing them.
