I love this. I immediately wanted to see how two cities overlap, but found the UI a bit difficult for this. I want to be able to see where's the best place for me and my friend in another city to meet up for lunch or something. I wish you could search a city and then edit the time you enter until you see two blobs overlapping....bingo lunch spot. https://d.pr/i/9DbVel

Unfortunately, to do this, I just had to keep entering new searches with incrementally new times. Anyways, just a feature idea. Nice work.