If I apply toothpaste to Fordyce spots for 8 hours will they go away?

See a dentist. See a dentist or an oral surgeon for an evaluation of the spots. Tooth paste will not cause these spot to resolve.
No. You will probably cause chemical burn which require a long healing time. These are cosmetic and can be treated safely if they bother you.
No. Fordyce granules won't go away from toothpaste, plus you'll possibly be swallowing extra fluoride.
Do you Believe it! You're dealing with a normal glandular structure in the outer layer of the mucosa of the mouth. Toothpaste is not designed or effective for this. You can try laser removal but these structures can regenerate just like any component of the skin or mucosa.