Ajax, I did read that too, but it does depend on the thickness of the laitance... ours was seriously difficult to remove (and it's all I have to hold on to right now to get the moisture levels down). The difference in the two textures (unsanded vs sanded) is staggering.
5.2 The effect of removing laitance. In the areas tested no effect on drying times was apparent whether the laitance was removed or not. It is acknowledged, however, that this tested a screed produced with a single sand source and different screeds may produce differing thickness and densities of laitance.