So, I opened up the "example images" folder and noted what one of the files was named: Humpback Whale.

I opened the start menu and typed "whale" into the search field - no results

Eh, no hits? Yeah, that's great. I clicked the "Search Everywhere" but it was equally empty. So I took that screenshot and saved it in Public pictures to move it to my Mac.

After having moved it over, I trashed the file and emptied the Recycle bin. Now, after over 30 minutes, the search result for "whale" is "Screenshot-Whale", but when clicking it, it obviously can't open it, since it doesn't exist. The original Humpback Whale image is still not found by the search.

So, how often does Windows index the content of the HD? Every hour?

This is really meager in comparison with spotlight that indexes everything live and every search is live.