I think that’s far too long to be honest.
I use a foil shaver (Andis TS1), against the grain, my head is baby smooth and within 12 hours I have to shave again.
In my opinion, as soon as you can start to feel stubble, you need to shave again, otherwise the difference between the SMP and your hair will be obvious.
My hair becomes much darker, even after 6-12 hours from shaving.
The shade of your SMP should match the shade of your hair when it’s shaved down, against the grain?