If you create a session in an ILT activity that has a start date that is different than the end date, you will encounter this within the course topic activity area for the ILT (see screenshot):

Instead of the session start/end date being rendered you just see the name of the language string it tries to render. The problem is, sessionstartfinishandtime is a non-existent language string in mod/facetoface/lang

However, this string does exist: sessionstartfinishdateandtime

I think that line 2270 (Totara 2.5.6) in mod/facetoface/lib.php should use the sessionstartfinishdateandtime string instead of the failing sessionstartfinishandtime string. This is at least the workaround I would suggest for the time being, as it now renders as the following (see screenshot);