The following options are available for specifying a fixed lunch break at a particular time.
Time request
A particular period (e.g. period 6) can be excluded from lesson scheduling using a block (time request -3).

Lessons
You can define a 5-period lesson (assuming a 5-day week) with the subject of 'Lunch', place this manually in the lunch period (e.g. period five) and either lock it there or have it scheduled automatically, e.g. in period 5, 6 or 7. The advantage of this variant is that the word 'Lunch' will actually be displayed in the lunch period.
