Summarize the following:
After you've applied the last coat, leave your tile undisturbed and let it dry for about 2 days. Avoid stepping on or touching the tile until it has tried completely. If you accidentally touch or step on the tile before it's dried, check it for smudges. You may have to apply an additional coat of paint and let it cure for another 48 hours. Once the tile has dried, peel off any painter's tape and check your tile for imperfections. If you see any smudges or uneven areas, or if you're not satisfied with the color's brightness, apply another layer of paint and leave it again to cure. With a paintbrush or roller, use long, even strokes to coat the entire surface in paint sealant. Let the sealant dry for about 30-60 minutes between layers before applying an additional coat. Re-apply the sealant every 6 months to protect your tile and paint coats from damage.

Summary:
Let your slate tile cure for 48 hours. Peel off the painter's tape and inspect your work. Apply 2-3 coats of a water-based urethane sealant. Finished.