I have updated and corrected the post to reflect the proper sunset time.

J Fincannon: Don’t blame ISRO or its engineers for that date. I came up with it simply by adding 14 days to the landing date. It was my guess, based on very shallow data.

Thank you for the clarification however. I guessed because I really did wish to know the exact moment the Sun would set and the missions would end.

I do not know where they are getting this date.

For a pefectly smooth lunar surface, the center of the Sun goes below the horizon on Sept 4 at 17 GMT. The “top” of the Sun goes below the horizon by 18 GMT.

But including terrain, I calculate they will end their mission on Sept 4 at 8 GMT.