'Morning-only' subjects
Some schools like to always teach a particular subject in the morning ... or always teach it in the afternoon. This rule may be school-wide or just for specific years.
A popular example is teaching Maths (and/or English) in the morning, in lower years.
You can tell TimeTabler you wish to do this, as follows:
Set-up your Rule(s)
You do this on the 'AM/PM Subjects' page of the Timetabling Rules Panel, which is described here and in the help buttons on the Panel itself.
Research
For some of the research on this, to help you decide if it is right for your school, see Research on the Effects of Timetabling
By the TimeTabler Team