Setting up Periods

Periods are your week's time grid — every other part of Timetabler (unavailable times, locked lessons, department meetings, generated results) is expressed in terms of Periods, so this is the first thing to set up for a new school.

Two ways to see this page

The Periods page has two views:

• New Schedule Configuration — a quick generator: pick your days of the week, how many periods per day, a start time, a default lesson duration, and a default break duration, then click Next: Edit Matrix. This builds an initial grid for you to fine-tune, it doesn't lock you into anything.
• Edit Schedule (matrix view) — the grid itself, one row per day and one column per period number. This is where you actually shape the week: click a column header to change that period's type/duration for every day at once, or click an individual cell to change just that one day's version of it.

Once you have any periods saved, the page opens straight into the matrix view. Use New Config in the matrix view if you want to throw everything away and start over from the quick generator.

LESSON vs. BREAK

Every period is one of two types:

• LESSON — a normal teaching period. Its duration is fixed to whatever "Lesson Duration" you set (all lesson periods share one duration; there's no per-period lesson-length override).
• BREAK — nothing can be scheduled here. This is how lunch breaks (and any other break) are represented, and it's a genuine hard constraint: the solver will never place a lesson on a BREAK period, full stop. Unlike lesson periods, you can give a BREAK a custom duration per column or per cell (e.g. a longer lunch break than your other short breaks).

There's no separate "lunch break" setting anywhere else in the app — marking the right period(s) as BREAK is how you configure lunch (and any other break).

Inactive cells

A cell can also be inactive — toggled off via "Deactivate" in the cell-edit dialog. An inactive cell isn't saved as a real period at all; it's just a placeholder in the grid so a day with fewer periods than your longest day still lines up visually. Use this for, say, a Friday that ends two periods earlier than the rest of the week.

Why period order matters beyond just chronology

A few things elsewhere in the app depend on periods being contiguous and correctly ordered within a day, not just on their clock times:

• Double periods: a Lesson with duration = 2 needs two consecutive periods on the same day. The solver actively prevents a multi-period lesson from being scheduled so its occupied range would spill across a day boundary (e.g. the last period of Monday into the first period of Tuesday) — so a poorly-ordered or gapped grid can make an otherwise-reasonable double-period lesson harder to place than it needs to be.
• Max span per day / gap-related soft constraints (if you enable them on the Constraints page) reason about "first active period to last active period" and "gaps between periods" in terms of period order within a day — an unnecessarily sparse or oddly-ordered grid changes what those settings actually measure.

Saving

Save Changes persists only the active cells in the current matrix — anything left inactive is simply not written as a period.

Saving matches each cell against your existing periods by day + start time: if a cell's day and start time already exist, that period is updated in place (same ID) rather than recreated — so editing a period's end time, type, or duration is always safe and doesn't disturb anything referencing it elsewhere. A cell whose (day, start time) combination is genuinely new gets a new period, and any existing period whose (day, start time) no longer appears anywhere in the saved matrix is deleted.

That last part is the one to be careful with: if you change a period's day or start time (rather than just its end time/type), that's a new period as far as saving is concerned, and the old one is deleted outright. Anything elsewhere pointing at that old period's ID — a teacher's unavailable slots, a lesson's locked or preferred slots, a department's meeting slots — isn't updated to the new period; it just stops matching anything. Your next generation ignores those references and warns you about each one (a lesson locked to a period that no longer exists is not locked), and on the Teachers, Lessons and Departments pages they show up as (deleted) in the period pickers. Remove those and choose the new periods. If you need to reshuffle start times significantly, it's worth re-checking Teachers, Lessons, and Departments straight afterward rather than waiting for the warnings.