Yes, you can "try" an idea in a weekend, but it's only going to be a rough sketch, not a polished experience. You still need a team and months/years of effort to bring it up to the next level so it can get the billion dollar valuation. How many weekend projects have billion dollar valuations?

Edit: In reply to mkr-hn whose comments I cannot reply to for some reason... I believe that this thread was about a bubble and billion dollar valuations not weekend companies worth much less.