As a 5StarTeacher, you are in control of when your available Sessions should automatically expire in case they were "not booked". That's why created the "Session Expiry Term". This allows you to automatically set or change the expiry date and time of all of your Available Sessions at once.

The Session's Booking Expiry Date and Time is the date and time at which an unbooked Session automatically expires. You can set your Session Expiry Term to 2 hours, 4 hours, 12 hours, 24 hours or 48 hours before the start of every Session. Currently, each month you can change this setting only 3 times.

Why is this so?
This is so that Students can rely on booking Sessions with you if you keep this consistent.

Suppose you had set your Session Expiry Term at "2 hours", meaning all your Available Sessions would automatically expire 2 hours before the start date and time in case they were not booked, and you changed your "Session Expiry Term" to 48 hours, all your Sessions within the next 48 hours from that moment, would then automatically expire.

Case.
Suppose it's Friday evening but something unforeseen has come up for the weekend e.g. the babysitter has fallen ill and you need to stand in. You can then change your Session Expiry Term to 48 hours and all your "Available" Sessions will automatically expire. Note that previously "Booked" Sessions for somewhere during this weekend will not go away, you do need to show up for those as you made a commitment earlier. If that were not possible for you, you can choose to cancel those Sessions. Check out "Cancelling Sessions" in the FAQ section to learn more.

Case.
Suppose a Student asked you during a Session with her if you would be available tomorrow as well, at the same time. Now if your Session Expiry Term were set to 48 hours, that would not be possible. So here you can solve this by changing your "Session Expiry Term" to something like 12 hours, and then create a new Available Session for your Student so they can book it right away and everyone is happy.