Although the surface is polished, there is still generally always porosity, by saturating the impregnator for a period of time depending on each porosity of different stones , this will give the product an opportunity to go in to the polished finish and give the water and oil protection.
Ie, I soak each section I impregnate, for different times , very hard dense polished granites up to 20-25 mins /polished marbles - 10-12 min .
I will always test a spare stone, or in a discreet area for this timing, see how your stone reacts, does it go straight in or does it just sit up on top. This test then determines my saturation times for each section or stone type.
The most important part of impregnation is then to remove the excess, any product not taken in to the cappillaries must then be removed, I use old white towels to then buff the surface fully dry , before then moving on to the next section. Don't leave polished stones with a wet look finish, this can then cause you problems, smearing, dullness.
So, where does the sealer go? You remove it