Go with Breakfeast. The caterer can't screw up bacon, eggs, toast, and sliced fruit.
Take a specific day. St Patrick's Day is a great day and if you have if 3 days before March 17th - everyone is available. Green orange juice, Bagels, etc. Make it as feastive or low key as you want.
It takes tremendous push - direct door knocking and sell tables to corporations seating 8. $35 per seat - $240 a table. Insist on the key people to be there.
Lunch is a more expensive dish and people can give away an early morning hour easier than Mid day.
Regardless of which you choose, you have to push it to be succesful
