No, there doesn't have to be a huge buffer. If the meeting is, say, an hour long and the workday is 8-5 with a lunch at noon, then meetings can start 8:30-10:30 and 1:30-3:30.
> Meetings that are adjacent to lunch are fair game. They just need to start/end on time.
Well, it can work, of course. I often have meetings scheduled like that. I hate it, though, because it means that I either have to cut lunch short or skip it altogether. A meeting may start and end at a set time, but I'll still need 10-15 minutes before the meeting to prepare, and sometimes 10-15 minutes after the meeting to perform action items that can't wait (such as updating my task list, my work notes, etc.)
(Lest people think that I value lunch too much, in nearly every place I've worked, taking lunch was required by management. If it weren't, I'd always skip lunch so that I could have an 8 hour long instead workday of 9)
Meetings that are adjacent to lunch are fair game. They just need to start/end on time.