Now this has become two issues...when to use the back of the fabric which can now be referred to as the right side...and I do that when I need a lighter shade and can not find it.
But original title was "How do you know when to take a break?"
A) when I am frustrated. I just will not do good work when I am stressed, or frusterated, unless I have turned on some music I find relaxing, had a cup of tea, and am doing hand work...then they release the frustration and stress.
B) when I am interuped by phone, delivery truck, grandchild, company, husband...
D) when I have reached a particular goal, and have been "at it" for hours.
E)When my light source changes, so my eyes can adjust to new lighting source. Like day to night, or morning light in East window to afternoon lighting in West facing window, or when it rains and I need to turn on the lights...
F)When my body pains can no longer be ignored
G)When it is time to prepare meals...and as I am diabetic, that is a maximum of 4 hours per sitting.
H)When I feel satisfied that I have been productive enough for one day, and or need to read more directions to begin the next portion which has different construction methods or directions.
and I have a few other reasons (like end of the "sit n stitch", or group sewing session is over)...but this gives a good flow of thought.