I know there's visually a change for the time of day at grom, but why not the main island? It would be wonderful to skate the districts at night it would also possibly improve the Realism in the editor
Because they have to go and manually add lighting to every single object in San Van and adjust them so that they appropriately light the environment and have the right colour. They are working on it because you can see they've added lighting to certain areas like this wall in the rolling waves park.
They also have to manage things like dynamic lighting, how that will affect performance at night, any prebaked lighting the game may or may not make use of.
San Van is about X: 1.4km Y: 1.2km of urban environments, Grom is about X: 600m, Y: 500m with way less lighting to do. Hope that clears it up