Rushing the sourdough long fermentation process is a common mistake newer sourdough bakers make. I know I’ve made this mistake plenty of times!
The part of sourdough baking that must be learned through experience and can’t be learned through any amount of lessons is baker’s intuition. This intuition allows the baker to sense when to adjust a recipe on the fly because the dough doesn’t feel right or look right. And it also helps the baker judge when the dough is ready to shape and when it needs to be left longer, regardless of what the recipe says.
The timing for sourdough recipes is usually a general guideline and may have to be adjusted in your home environment.
Dough that is done with fermentation and ready to shape should be double in volume but it also should have a certain look and texture. The dough should have a smooth appearance, with a pillow-y appearance from the air built up inside, and should be only slightly tacky. See this quick video for a side by side comparison.
The batch of sourdough that is well fermented was fermented overnight then 8 hours at room temperature. The other batch of sourdough was fermented about 5 hours at room temp.
Note: It is winter and cold in my kitchen when I filmed this. During this season, all of my batches of sourdough are fermenting on the long side. I usually let them bulk ferment 7-9 hours at room temp. Adding warmer water (70-75 degrees) allows me to shorten the timing slightly.