If your guests will be there between 8 and 10 A.M., you'd better serve breakfast. If they're there between noon and 1, plan to serve them lunch (a cold cuts buffet is fine). If they are there after work, and it's for more than drinks, plan on feeding them dinner. If it's after the “American dinner hour” (which means after 6:30 P.M.), they will likely all have already eaten and only expect cake and beverages. Any other time, snacks are totally appropriate, and cake is required.