My baby nephews bday party is saturday but i work saturday and iam doing the cake. but if i decorated it tonight or tomorrow would it last as far as taste n stuff till saturday?

Yes, it'll be fine at room temp as long as no fillings are used that require refrigeration.

It will still be delicious Once it's decorated, no air gets to the sponge so it will still be moist on Saturday. In fact, some cakes improve over time.