How accurate is the window pane test? (breadmaking)
In my experience, the lighter the expected loaf, the more effective the windowpane test is.

The windowpane test will work best with high protein breads made out of very fine, or refined, flour with no gluten-interfering additives. This means "artisan" style loaves made out of bread flour, water, salt, and yeast. The gluten in these loaves is very well developed and they rely on this to create very light, open loaves.

If French bread is on one side of the glutinous spectrum, then a dense sourdough rye would be on the other. It would be very difficult to get a windowpane test to work with rye, because there is little gluten. It makes a very dense loaf.

Of course, your bread is going to be somewhere in the middle. 60% is a good ratio for standard sandwich types of bread. Any ingredients that will interfere with gluten development will make the windowpane test difficult. Coarse wheat flour will have less gluten and will cut the existing gluten; added fat will inhibit some gluten formation.

Either way, I wouldn't go by time. You want your dough to pull away from the side of the bowl and be "smooth and elastic". It should be less sticky and should spring back when manipulated. With a little practice it is easy to recognize this state while it is being kneaded and timing is no longer necessary.

Note

If the texture of your bread pleases you then the test isn't so important. If you would like to pass the windowpane test and make your loaves lighter and less crumbly there are a couple things that help:


If the recipe calls for fat, reduce it or leave it out
Fat gives tenderness and flavor. I often reduce it, but leaving it out may leave a flavorless loaf.
Use higher protein wheat flour
Bread should be made with hard red or white wheat. Soft wheat flour is used in Southern cooking that doesn't require as much gluten, such as biscuits.
Use finer wheat flour
The finer the grind on your wheat flour, the less it will cut gluten strands.
Add gluten
You can purchase essential wheat gluten. It is very helpful, especially with breads high in wheat flour.
Add acid
A small amount of acid helps with gluten formation. You can grind up a vitamin C tablet (ascorbic acid) or add a little citric acid. Sometimes I will use leftover orange juice, but remember to take into account the liquid and flavor that it will add.