For coordinate matching, Arc will likely be able to do the same as what it does with iOS’s photos library.

That is: It grabs all photos within the timeline item’s date range (because iOS’s API doesn’t provide filters for coordinates either), then it walks through those photos one by one, and determines whether that photo has coordinates that fall within the timeline item’s range.

Although if the Google Photos API doesn’t allow for access to coordinates metadata on photos, then that will present a problem. In that case, Arc would have to just show all photos that fall within the timeline item’s date range, without filtering for whether they were actually at that place / along that path or not.