When you are overworked, overstretched, and dragging, take a break.
Come back afresh and take the plunge into the work again. You will be more focused and determined.
Taking a break gives you the needed mental and physical space. Otherwise, you will feel gloomy, disillusioned, and the results would be the same.
There can’t be any rule, and you should know when your body and mind are asking for off time.
Whenever you need, take a break.