Your session duration could be adjusted through a session's settings.

To do this, can go to the Calendar section, and then click on the small gear icon on the upper-right-hand side of the session card. Then click on Edit Session.

This will open a page for you to be able to change your session's settings. Click on the pencil icon in the Tell us about your sessions section.

The option to change your session's duration will be there as seen below: