[aeturnum]

From a history point of view, early mainframe programmers were required to be night owls. Mainframes were expected to be running all day doing the calculations they were purchased to do - the only time they were allowed to be idle for development and maintenance was after the close of business. This is also the source, to a certain extent, of the unusual freedoms programmers often enjoy within organizations. They needed to have unusually free access to the most expensive equipment (and the building in general) and weren't supervised in person by the usual hierarchy of bosses.[1]

[1] From The Computer Boys Take Over, a very good basic history of the professsion: https://www.goodreads.com/book/show/9247209-the-computer-boy...