Dynamic time and weather is something that quite a few games in the racing genre aim to have included, but Kazunori Yamauchi has stated that neither of these will be present within Gran Turismo Sport. The confirmation regarding the lack of the dynamic features comes from an interview GTPlanet conducted with the developer, where he stated this decision was made to favour framerate and quality.
“We opted to not have the transitions in the race this time in order to raise the framerate and the quality of the image *during* the race. So the user will be able to set that before they enter the race. So you’ll still be able to have night races, morning, races at dawn, dusk, and so on.”