New player looking for 5E one-shots this weekend on classic FG

As I said in the title, I just got FG because I want to be able to play D&D with some of my friends. However, we're all new to FG (and I'd be the DM), even though I've played D&D for a few years now, so I wanted to try a game or two to get acquainted with the platform. I've spent some time trying to figure out the platform already, though I'm nowhere near an expert yet.

I'm a bit on the younger side of the hobby (18M), so I wanted to mention that as a disclaimer. I'd be down for any style of play, as long as people would be a bit understanding if I run into some trouble.

How long would the one-shot run? One session for how many hours??