I play in Challenge mode.
The only way it gets dark in this map is when it rains.
Challenge mode and Franchise mode are essentially the same thing except one can be played offline. The intent behind them is the same.I have not played in the Challenge Mode yet. But, I do think that it should work like the Franchise Mode. Therefore, I don't believe that it is intended for the sun to never set. I would suggest you report the issue.