Monday is Water Seed rehearsal day at Lou Hill’s house—every Monday at 11:30 a.m. The strictly observed regimen is just one example of the New Orleans funk-pop band’s quest to excel.

Water Seed’s final rehearsal in the month of May happened on the Memorial Day holiday, when many people were taking the day off. “Not too many people gig at 11:30 a.m. on Monday, so it’s a great day,” ...