I've noticed that the Big 6 novels all seem to release on a Tuesday or Thursday. The article and comments presented speculation, but nobody seems to know for sure. I'm willing to bet that whatever the reason for the Tuesday-Thursday rule, it has its origins in the pre-digital era, and is still followed just as a leftover custom. Maybe it had to do with book reviews being in Sunday and Wednesday papers, or some bookstores being closed on Sundays and Mondays rather than Fridays and Saturdays, or something like that.