The one-off day-night Test between South Africa and Zimbabwe, starting on Tuesday, will be staged under experimental playing conditions.
The International Cricket Council gave permission to Cricket South Africa to stage a four-day Test.
There are several variations from standard Test playing conditions.
Play will be scheduled for six-and-a-half hours each day, half an hour more than in five-day games, with 98 overs due to be bowled in a day, instead of 90. As in five-day games, an extra half hour can be added in order to complete the overs.
The first two sessions of play will be two hours 15 minutes each, instead of two hours, with a 20-minute tea break instead of a lunch break after the first session. There will be a 40-minute dinner break after the second session.
There is no provision for time lost to be carried over to subsequent days.
The follow-on can be enforced with a lead of 150 runs, compared to 200 runs in five-day games.
Play will start at 1.30pm (1130 GMT) each day. The sunset in Port Elizabeth will be between 7.30pm and 7.31pm on the four days of the match, half an hour into the last session.
It is the first Test match since 1972/73 to be scheduled over four days. Until then, Test matches were played over varying numbers of days, from three to six - and on a number of occasions were "timeless", played over an unlimited number of days until a result was achieved.
The last timeless Test, between South Africa and England in Durban in 1938/39, ended in a draw after ten days (one of which was rained off) when the England team had to catch a ship home.
Since 1972/73 Test matches have been standardised as five-day games, although a match between Australia and a World XI in 2005/06 was scheduled over six days. It lasted four days.
The South Africa-Zimbabwe match will be the eighth day-night Test and the first to be played in South Africa. Four of the previous seven day-night games have been played in Australia.