I'm glad that you feel that way! I'm a big proponent of work-life balance, so being able to be productive enough through the day so I can leave without feeling guilty is a huge plus. I wish more companies held similar views.
Hopefully, if there are enough productivity gains and as the startup transitions out of super-lean mode, you could represent that increased productivity with a shortened work day/week!
We believe that when you come to work you should make the best of those hours so you can spend the evening with your family, friends, or just relaxing.