Yes, if you are a teacher or presenter, you can extend the class duration while the class is in progress.  You can do this by clicking the clock button located at bottom right corner of the Virtual Classroom (see Figure 1.1).

The Class settings window with a dropdown list titled Extend session will open (see Figure 1.2). You need to click the dropdown list to select the time by which you want to extend the session or class.  When you have selected the appropriate time, you need to click OK to extend the session or class duration.

                              Figure 1.1

                                 Figure 1.2