I am much more concerned about the volatility of small sample size. Sickdays inside a single building can be easy effected by single individuals. Imagine if either the control or test work place has an employe who is carrier for the flue but with limited symptoms. Such event would invalidate the experiment if one is simply looking at the number of sick days for data points.
At best, I think one should view this experiment as a preliminary test in order figure out how to do a real test with a larger sample size.
Not just small sample size, it's also biased. FTA, "The year-long experiment will compare two factions of municipal workers." Obviously, the results would be very different for various professions. For people who just push papers, yes they can be 25% faster to get 2 hours more with their family. However, what happens with the service industry? If the bus drivers work 2 hours less, then there will surely be less busses on the road.
At best, I think one should view this experiment as a preliminary test in order figure out how to do a real test with a larger sample size.