Setting up short session 5e

[Yakmala]

My youngest just returned to in-person HS and discovered there is a D&D club forming. For his age, he's a pretty experienced DM and he wants to help out. Problem is, this school is doing its club meetings during lunch hours, rather than after school. Given the time going to and from classes, the best they can hope for is half hour sessions. He's assuming a few experienced players and good number of total beginners.

So, the question is, what is the best format to run 5e with such a short time frame per session? Missions/jobs/quests need to be short and succinct. Battles should probably run no more than 1-3 rounds. The DM will have to balance allowing players to express themselves through roleplay with a small window to give everyone time to have their moment.

I think it's a given that adventures will span multiple sessions, but each session should add progress to the overall goals.

So, suggestions? Things to do and things to avoid? Tricks and techniques to make an impact in a short amount of time? Any classes to avoid in the interest of time (like druids or necros with swarms of summons)?

[Havlock]

Given the serious time limits and that club members will likely come and go or not make it everyday, I'd recommend thinking of it more like a dnd workshop. Theory craft, teaching the rules, how to DM or role play... maybe some very quick pre-built battles to demonstrate the mechanics.

Ex:
Monday, talk about tanks. What they do and how they do it and why you need them.
Tuesday, theory craft some concepts
Wednesday, everyone build their favorite tank
Thursday, everyone share their build concept
Friday, take them for a quick spin slaughtering a pile of orcs or whatever. Maybe make it a unique thing where the group needs to stop x enemies from getting to the other side of the playing field.

IMO, running a campaign under your constraints would be nearly impossible.

[Kurt Kurageous]

KISS obviously.

An old school dungeon with a map given to the players/put on the wall/screen is a good start.

Consider using pregen characters from anywhere.

LMoP goblin hideout map is a good start, but tough to play. Consider nerfing.

He should hold on to all char sheets at end of session and redistribute based on who shows up next time around.

He needs more than one person to run a group of any size greater than four.

From a guy who ran an after school club for three years, but we had more than 30 minutes.

[Sorinth]

My suggestion for the adventure/campaign structure is that the players are looting a mage's tower. Each floor is designed to be cleared in the session, so basically you start at the staricase down and finish the session when you find the staircase up. Every floor is a mix of combats, puzzles, and treasure. Thanks to magic each floor can be as big or as small as it needs to be and maybe even it's own set of physics or permanent magic effects.

Since I know puzzles are sometimes controversial my suggestion is to make the puzzles solvable by trial and error but at a cost for each error. So if you need to press 3 buttons in the right order to unlock the door to the next level, you can solve the puzzle by finding the clues and solving it, or you can just try every combination but wrong combinations fire off traps or summon creatures that then have to be fought off.

In terms of resting I would simply do something like you get a short rest after X floors, and a long rest after Y floors. This can be out of game automatic stuff or those floors of the tower are meant to allow resting, ie the floor is one room with a fountain, drinking from the fountain gives you a SR but water taken away for later use will lose it's magic.