@cs3000 - Even less than just one minute would be one minute every third day.

In the 1st paper that you hotlinked Glen Jeffery, University College London was the last named author. I the first 6 minutes of this video below he speaks about the every third day. I seem to recall from a different video that every 5 days is sufficient to keep the mitos. charged.

https://www.youtube.com/watch?v=BkciTZvR2eY

Edit - The red light works best in the morning.

Dosage, Time & Time of Day for Red Light Therapy | Dr Glen Jeffery Interview Clips