Each day of the upcoming inaugural four-day Test between South Africa and Zimbabwe in Port Elizabeth will need to have a minimum of 98 overs per day, as per the ICC's playing conditions. That is, eight overs more must be bowled every day than what is required in five-day cricket. Also, a lead of 150 will be enough to enforce the follow-on; in five-day cricket the mark stands at 200 runs.
To accommodate the extra overs, the ICC's playing conditions state that play will run for six and a half hours in all each day, instead of the usual six hours for five-day Tests. The home board shall determine the hours of play and duration of the sessions, with each session lasting a minimum of two hours and a maximum of two and a half hours. In Port Elizabeth, the normal hours of play are set to run from 1.30pm local time to 9pm, with the first and second sessions being two hours and 15 minutes each, and the final session running for two hours. An extra 30 minutes will be available to the fielding team to complete the minimum required overs each day.
Beyond the half hour of overtime, any remaining overs cannot be carried over to the following day unless there has been a stoppage for "any reason other than normal intervals" - rain breaks, for example.
Also, the last hour of play on the final day will officially commence only when 83 overs - it's 75 overs in five-day Tests - have been bowled on the day. In cases where 83 overs are bowled ahead of schedule, then the calculations for the last hour will be dictated by the clock, as is the case in five-day cricket.
The reduced follow-on mark is in keeping with the existing laws of the game, as already applied in domestic and other four-day first-class cricket.
The Port Elizabeth Test will also be played as a day-night game, with the pink ball under lights. That means the first break - for tea - will be the shorter of the two at 20 minutes, with a 40-minute break for dinner following later.
The match was handed Test status by the ICC in October, as a "trial". Then ICC chief executive David Richardson had said that the trial of four-day Test cricket would run until the 2019 World Cup, although participation in it is not mandatory. He expected the shortened version to be especially beneficiary to the lower-ranked Test teams.
"Whoever wants to play it can play it," Richardson had said. "The real value is [for] teams like Ireland and Afghanistan, even Zimbabwe who have not been at their best. Teams visiting, for example, South Africa, might be more likely to [take a detour to] play Zimbabwe in a four-day Test than they would in a five-day Test. So I think it has a number of advantages."