Although prime ministers have answered questions in parliament for centuries, until the 1880s questions to the prime minister were treated the same as questions to other Ministers of the Crown: asked without notice, on days when ministers were available in whatever order MPs rose to ask them. In 1881 fixed time-limits for questions were introduced and questions to the prime minister were moved to the last slot of the day as a courtesy to the 72-year-old prime minister at the time, William Gladstone, so he could come to the Commons later in the day. In 1953, when Winston Churchill was prime minister, it was agreed that questions would be submitted on fixed days (Tuesdays and Thursdays).

Can we conclude that are prime minister's questions known in advance?
no