When I apply grout, the grout gets pushed hard into the cracks to get all the way down the seperation. this is what you want. Then you trowel the excess of the surface at that time, not all will come off. Then after 20 minutes, I begin with my fresh water wipe down to remove the grout and to actually smooth out the grout in the cracks. I have seen some people use the handle end of a tooth brush to carve a nice smooth valley in the grout line. Just alittle wiping with a all cotton cloth, like a diaper is great. You will clean the rag many times to get the haze off the surface of the tile.
With the haze gone, then the curing process take hold. The shower or tub should not be used for three days during this process. It is recommended, but I am sure people do not do this, is to mist the grout with an atomizer three times a day during this curing process. I pass this on to my customers, but who has the time for this to happen as directed?
Since you replied that the tile does have a glaze, then you should be OK. I answered your question and said what I did because you did say it did NOT have a glaze and was porus, which would make your situation dire.
Good Luck PS consider applying a silcone seal to the grout when your done. This will save you allot of cleaning and the grout turning green or brown. It does not need to be on the tile. The glaze makes it non porus, the silicone will make the grout non porus also. Apply it accordingly to instructions.