I often need to add up the duration of voiceover files that I have created for a client, or using audio to determine the overall duration of a presentation. A quick method for adding up the total audio time within a program can be to select all the audio files within a folder. At the bottom of the folder, the total run time duration of the audio files should appear, along with the total size of the selected files. Note that you may have to select “more details” to display the detailed rundown on the folder contents (that include total duration.
While this will not necessarily represent the total seat time of your presentation or elearning course, since you will likely need to include time for the user to read text screens, it will give you an idea of the duration of the voiceover components.