From there, you go to Flexible Timetabling 

Flexible timetabling allows students in particular years to be permitted to arrive later to school when they have free periods, and leave early if they have finished their last class for the day. Depending on how the timetable is structured, Timetables provides a range of options to configure any classes that should be ignored from a student's timetable, excluding them when determining which class is the first or last lesson for a day.

Allowed School Years: Choose year groups 

Include Inclusion or Excursions 

Permission for flexible timetabling arrangements can be managed on a student by student basis, so that students who have not received parental permission for flexible timetabling arrangements are prevented from scanning in/out even if their year group is eligible for flexible timetables.

Enable Individual Student Selection switch on to Yes.