Education block - How to allow gaps in class timetables
discontinuous educational block
Please see this article Education block - Checking of gaps in class timetables
for better understanding, how ASC Timetables places lessons into automatic "Educational block". 
If you wish to allow gaps in classes timetables (and it means also in students timetables) you can set in Class - Constraints - Advanced - Discontinuous educational block.
See also:
Education block - allow some classes to come later or to leave school earlier.
Class can have max 2 gaps per day
Student can have max 3 gaps per day
 
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