12 hours? You’ll be lucky to get any of that off. You may have to remove it all and start over. Did you use grout release before you grouted?

Deb after 12 hours you can certainly clean residue. If your initial clean up was done properly any residual grout should come of with a light pass with a sponge or buff off with a cloth. Without a photo and the product used it would not be possible to advise further. There are many variables that need consideration.

Here’s a pic for reference: The grout used was Maipei Keracolor Sanded Grout

Use a cheesecloth for the grout on the tiles now

Judging by your photo there is a good chance residue will buff off. Let us know how you make out. There are more aggressive approaches if needed. I'm impressed with a DIY'er undertaking such a difficult mosaic to grout. Especially black on white. Hope you're successful.