can I make fresh pappardelle several hours before cooking or do I have to roll, cut and cook immediately?
I have made fresh pasta ahead of time you just have to make sure its well floured or it will stick together. Cover with a clean kitchen towel make sure every piece of pasta is separate. It really depends how many hours you are talking about but 1 or 2 should be fine.
It sounds like you actually just made the dough and want to wait to roll and cut it. Just keep it wrapped tight in saran wrap in the fridge, it will stay that way for up to 2 days in my experience. It actually makes it better I think, because it gives the dough a chance to rest a bit.
When I've taught pasta making classes, I make several batches of the recipes I'll be teaching ahead of time. Sometimes we don't cook any of the dough we mix up in class, other times, we make some of each so we can discover and discuss the textural differences in the two.
That said, you definitely can make your dough ahead. You can even roll and cut it, but need to keep the moisture in it, without allowing it to stick together. that can sometimes be tricky.
When I was a little girl, my Aunt Rachel would have the ravioli dough rolled out on the kitchen table waiting for me to get there to help her fill them. She must've had a sixth sense to know when we'd come driving up, because that dough was never dry -- always supple, and chiefly responsible for my love of fresh pasta to this day.
You can absolutely let pasta rest and dry before cooking. I used to hang the cut strands over the backs of chairs a few hours before serving it. Just don't let your guests sit in the chairs while it's still hanging out. Humidity is a factor but not one that alters cooking time much.