I remember I spent a year up there (had a great place facing Elliot bay right under the Needle).
I remember it stayed light reallu, really late.
IIRC, it was late until almost 11 on the night of the Summer Solstace.
I don't know why (the owners don't have lights on) but for some reason these cams stay light longer. I am in sorta downtown Seattle, and when it's dark here, these cams are still light.