Most 40ths here run as standing receptions rather than seated dinners, and it's the format we'd recommend. People circulate, the room stays loud, and nobody's stuck next to the same person for three hours.
A typical evening:
From 19:00 — Arrival drinks on the terrace, canapés circulating
20:00 — Food service opens: grazing tables, a live BBQ, or a smash burger station
21:30 — Cake, speeches if you want them, cake if you'd rather skip the speeches
Later — Music, bar, the terrace under the trees
We can also do this as a seated dinner, a long-table lunch, or an afternoon that rolls into an evening. Tell us what you had in mind.