Sounds like you are on a good track with Brian's AAW offerings. In terms of the official 5E modules by WoTC, the only one that fits your needs and has fit that for a long time is LMoP -- the Lost Mines of Phandel. Truly is-was designed as an introduction adventure, one of the first 5E products that came out. Personally, my recommendation is create your own entire one-shot adventure. Use some of the free graphics in Roll20 or buy 1 or 2 marketplace Art Packs (such as a Gabriel Packard map pack, and a BrassBadger token pack, for example). Put it ALL on one large PAGE of roll20 (that you create in advance spending a few hours of prep time). Page size of 50x50 is my recommended starting size for you if making this. You're making Pre-Gen characters already, you will place their pre-made Tokens on the page (top left corner, recommended) and have everything ready for start-time on game day. An adventure of 3 locations ("3 maps") will be MORE than enough for your time slot. To me, the adventure can be as simple as: City Gates > Forest > Heart of the Forest encounter. (1, 2, 3). Put an NPC guard at the city gates. Put an NPC (a hunter?) and 1 beast monster in the forest section (sabre-tooth tiger?? large spider?? ettercap??). Put a "boss monster" in the Heart map for the finale' (Owlbear??). Done! Make up the verbal descriptions and clues, as you go along, just dream about it for a while in advance to have some ideas ready depending on what the players say-do. For example maybe the Guard at the Gats will say "There is a reward 100 GP for a feather from the mysterious owl that has been reported in the nearby forest." And I promise, in my experience that's enough material for a 2-hour one-shot with new players and starting GM.