In 2018 the warm-up period was reduced from 5 minutes to 4 minutes.
But there had been an earlier change. Before the 1 May 1989 rule change, the Rules allowed players to knock up separately for 2.5 mins each if either or both players wished to do so.
The first player was allowed an extra minute to warm up the ball, so it could have been a 6 minute warm-up period in total!. Credit WSL