I would seal the face of the tiles, but again... be carefull not to seal the sides inside the grout lines. If you get the sealer in the sides you may not get a good adhesion of the grout to the tiles. Sealing the face will allow you more time to remove excess when grouting without ruining your tile.
How long does mortar take to dry? I was going to grout last night and I noticed that the mortar was a little "gummy". I checked again this morning and it was the same texture. I laid the tile on Sunday.