Subjects time-off

In case, that the subject can be taught only on specific days or periods, you can use the "Time-off" setting and allow or block positions for lessons in this subject.

Use menu Main and click on Subjects, select the subject and click "Time-off".
In the new dialog you can change the state of each cell by clicking on it to "Available", "Conditional" a "Not available".
If you click on rows or columns headers, you can change the state for all cells in the row/column.

E.g. - if all swimming lessons can be only on Monday, Wednesday and Friday afternoon you can just change "time-off" setting for subject "Swimming":

Or, if you need to lock all lessons from one subject on first period each day, use this setting:

Note:
- in case, you need to block subject on positions only for some classes/teachers, use: Biology has to be in the afternoon in certain classes and in the morning in other classes