On the contrary, the 9-5 concept has never applied to the vast majority of working humans on the planet (agriculture, health, factories, sales, even most offices don't keep those hours). With growing communication across time zones, their difficulties have only recently become more obvious, previously this sort of communication was rare, now it is becoming commonplace.

The solution to not being sure if someone is working at a given hour is to schedule a call, preferably using a sane shared timekeeping standard which doesn't change hours at the whim of politicians.