Hi Manon,
a few suggestions:
– work in really small groups, so you can move on – instead of waiting for several tables to finish their discussions
– do not just set up a timeline, but use a visible timer as well – so people know when they should finish and you don’t have to scream to silence them
– make the challenges really comprehensive and don’t try to touch on too much serious content in just an hour
– be clear in expectations on your role: you can’t cover all tables – so stick to facilitating the overall process instead of individual tables
– a hand-out with some contents and the stated challenges might work, as does a clear instruction for one person per table who could take some pictures and share them
– be sure to put some table cloths on the tables you use, 350 people playing with LEGO make noise!
– and yeah: have some co-facilitators in the room, or brief a few persons – use them for keeping track on the process / a good flow in the meeting as well, instead of putting them on a table close to the participants
Want to know more? Feel free to reach out: wiro@zinindezaak.nl
Good luck, Wiro