Do you think Starfleet ships (or stations, for that matter) observe weekends? Days of the week rarely merit mention at all, except for the NX-01 having movie night on Tuesdays. "Chain of Command" (TNG) shows the 1701-D having only three shifts (though I don't think it's ever explicitly stated that they're only eight hours, so the shifts could be arranged in some way that allows days off). It's hard to imagine the crew working every single day without burnout. Though maybe various modern conveniences (the replicator, etc.) remove enough of the other responsibilities that most people today have in their lives that they can fit plenty of relaxation into their daily off-hours?