Hello, Brent:
That depends on your type of beard, how often you shave, and on the blade. Some gentlemen use the same blade for a week, some four days, some five, and so on.
As a general rule, despite using Feather and Gillette 7 O'Clock "Sharp Edge" yellow packs, two of the sharpest and best blades made, I think, I change blades every three shaves. I have a heavy beard, yes, but even if I did not, I still would change every three shaves.
I have come to accept from my own experience that, in general, the blade begins to lose its effectiveness after the third shave. This is not scientific, but my experience, as I said.
So, my good friend, I suggest going with the three-shave-per-blade set up.
Regards,
Obie