When the team is tired, shorten the meeting, not the standard.

Tiredness is a real constraint, and the wrong way to answer it is by lowering what counts as good. Cutting the standard feels generous for an afternoon and leaves everybody with worse work to live with, while cutting the time spent talking about it costs nothing anyone values. One of those is kindness and the other only looks like it.

When your group is flat, take the meeting down to its two essential minutes and let people go. Keep the thing itself exactly as demanding as it was. You will get more out of a short day than a sloppy long one.