Pretty sure in the early days they started about 3pm to allow for people who did half days on Saturday before the 5 day week. I'm reading the history of Grand Finals books and there was one around 1940 where they said the start time was brought forward from 2.45 to 2.30pm
perhaps they followed start time of the game played in the mother land?
has the traditional start time fro English soccer always been 3pm?