If a bard (or anyone skilled in Performance) wants to earn a living during downtime without paying for any lifestyle expenses, how long should the performance last?
Chapter 8 in the PHB states the following about Practicing a Profession during downtime activities between adventures:
You can work between adventures, allowing you to maintain a modest lifestyle without having to pay 1 gp per day (see chapter 5 for more information on lifestyle expenses). This benefit lasts as long you continue to practice your profession.
Furthermore, for bards or anyone who is proficient with the Performance skill:
If you have proficiency in the Performance skill and put your performance skill to use during your downtime, you earn enough to support a wealthy lifestyle instead.
The top section on Downtime Activities states:
at least 8 hours of each day must be spent on the downtime activity for the day to count.
Since downtime activities can include crafting or researching, I can totally see how that would require 8 hours of work each day, but performing? 8 hours of performance would equate to non-stop playing and/or singing in a tavern from 6PM to 2AM. That sounds excessive, no?