Biology has to be in the afternoon in certain classes and in the morning in other classes

If you define time-off for Biology, it then affect all Biology lessons in all classes.

If you do not want to affect all lessons, you can leave the timeoff empty and define advanced cardrelationships like:

The cardrelationship says that there can be max 0 - meaning no biology lesson on the marked periods in the selected classes(5a/5b). So in other words biology in these classes can only be on the unmarked positions.

You will probably want to define also other similar rules for other classes that has to have Biology on different positions.

Note:
- you can change max 0 to max 1. This can be usefull if the rule is too strict for your timetable and perhaps you can tolerate 1 biology in the marked area, but not two in any given class. (the rule is applied to each selected subject in each selected class separatelly)