Why not let your employees choose? From what I’ve seen single people love 4x10, people with kids don’t. 2 extra hours a day means my kid can’t possibly make it to practice in time 4 days a week.
9 hours maybe, but 10 hours? I'm a software engineer, I can't produce quality work for 10 straight hours. Most good, solid work gets done in a 4-5 hour period. 10 hours in front of a computer isn't good for anyone.