Assuming they didn't screw up the tile by walking on it before it "set," it shouldn't be much of a problem. In fact, if the grout was set while the morter was still curing, it'll all bond together and be quite strong!
Avanti Tile & Stone
"If you love wealth greater than Liberty, the tranquility of servitude greater than the animating contest for freedom, go home from us in peace. We seek not your council nor your arms. Crouch down and lick the hand that feeds you. May your chains set lightly upon you and may posterity forget that ye were our Countrymen."