Windows as a metaphor for the human condition

What is the significance of Klara and Josie watching the sunset together?

Watching the sunset together gives Klara and Josie a chance to bond.
This ritual brings joy to them

I agree with gloriak in that their watching the sunset from her bedroom window each day helped them to bond. I would also go as far to say that the sun nourished them both--providing energy to Klara's solar cells & sense of serenity & predictability to Josie. With all of the uncertainty of Josie's illness, watching the sunset with Klara each night allowed her to focus on something beautiful & reliable in a stress-free setting while being with a friend who offered her unconditional support.

I didn’t understand this metaphor at all. I’m interested to see how others answer this question.