whipped cream icing beforehand vs right before serving I found a recipe of a chocolate poke cake with chocolate ganache in the holes and a whipped cream icing that it's supposed to be only on top, and then with pecans and chocolate flakes and dulce de leche.

The direction say the cake should be served right after making the icing. Is there a particular reason for this? 

I'd like to eliminate the dulce de leche and I wonder whether the cake can be done (decorated I mean) a few hours before serving and kept in the fridge.

Can the addition of confectioner's sugar to the whipped cream improve its lifespan of a few hours (and compensate the absence of the supersweet dulce de leche)? thanks
Whipped cream can be made with unflavored gelatin, so that it will hold its shape for hours; that is how bakeries do it. I did not find it difficult to do the first time I tried it, and was really pleased at how reliably it held up.

http://ourbestbites.com/2015/11/how-to-make-stabilized-whipped-cream/

There are other techniques, but this is an example of how to do it.