Can You Carve It After 5 Days?

Yes, but you will need either hammer and chisels or an electric hand-grinder. A mortar cutting disk in a hand grinder will effectively remove the surface of cured material. This is also excellent for cutting grooves for preparing the surface for another layer. Particularly with large sculptures. Drilling is possible - with a new sharp Tungsten Carbide drill-tip - but wait till it is mostly cured. And please DO wear a dust-mask!