Surah An Nahl Tafseer

وَلَكُمْ فِيهَا جَمَالٌ حِينَ تُرِيحُونَ

And there is beauty in them for you, when you bring them home in the evening.

which is when they are brought back from the pasture in the evening.

This is a reference to how their flanks become fat, their udders fill with milk and their humps become bigger.

وَحِينَ تَسْرَحُونَ

and as you lead them forth to pasture (in the morning).

meaning when you send them out to the pasture in the morning