Hi musicspirit.
While date and time metadata for a photo is editable in the Photos app, the date created and date modified for files and folders in the Finder are not editable. As a workaround, you could try this:
1) Open the Photos app. From the sidebar on the left choose Photos under the Library setting and then the Days tab at the top of the window.
2) Choose a day. Click one photo from that day and then hold the Command key and click all of the photos you want in a new folder.
3) Under the File menu at the top of the screen, choose Export. You'll get options to either export the photos as you currently see them, or to export the unmodified originals. The difference here is that the unmodified option would discard any edits you may have made to the images in the Photos app.
4) A window with options will drop down. Don't change any of them. Just click the Export button.
5) You'll get a Finder window that will allow you to choose where the images will be exported to. In the lower left corner of that window, there is a button called New Folder. Navigate to where you want that new folder and then click New Folder.
6) Name the folder with the date or date range of the photos you are exporting (or any other way you want to organize) and click Export again.
You'll end up with a new folder with all of the images in it and the folder named according to your wishes. Be aware that doing it this way will create copies that will consume storage space. But if you prefer to organize your images outside of the Photos app, this is a good way to accomplish that.
Cheers.
