The reason behind that is the timing of the two matches, where the South Africa vs Afghanistan match in Trinidad is a day-night game (starts 8:30 pm local time, June 26) and the India vs England semifinal in Guyana is a day affair (starts 10:30 am local time, June 27).
T20 WORLD CUP: Schedule | Points Table
June 28 is the travel day for the two teams that make it to the final, which will be played on Barbados on June 29. So if the day-night match between SA and Afghanistan can’t be completed because of rain, it spills over to the reserve day on June 27. But because June 28 is a travel day, the India vs England day match on June 27 will have to be completed on the same day, and for that almost four extra hours have been allocated to the second semifinal.
According to accuweather.com, the forecast for Thursday morning in Guyana has 88% chance of rain and an 18% chance of thunderstorms.
In case rain plays spoilsport, the second semifinal will have another 250 minutes, which gives umpires eight hours to finish the match.
However, in the eventuality that rain leads to abandonment of the match, then the team that finished higher in ‘Super 8s’ will progress to the final. This playing condition applies to both the semi-finals.
Based on the above, if there is no result possible in both the semi-finals, then India, who topped Group 1, and South Africa, who topped Group 2, will advance to the title clash.