The offset pattern definitely helps those who can't access the game too often or every day, or at regular intervals.
It's particularly important for the claiming period, because if you fail to claim your winning bid, you lose half your gil.
I could perhaps see them shortening the bidding period, to three days, with a four day claim period, to fit that 7 day cycle, that still allows more than two days per phase, and crucially the four days for claiming so you don't lose your gil. I do agree you'd have to be very specifically unlucky to be unable to log in for four days straight due to working patterns.

However... there's no pressing need to shorten it other than the fact that people are impatient. Two additional days isn't going to hurt.