This bread recipe requires an active sourdough starter. It may not match whats written in your favorite sourdough cookbook or whats shown in that video you saw online.
The Science Of Sourdough Starters Sourdough Starter Sourdough Bakers Yeast
If you have a process you successfully follow regularly then stick with it.
. Depending on the virility of your starter you may want to add 12 tsp of commercial bread yeastIt is traditional for French loaves to contain a mixture of commercial yeast and starter. This method for maintaining sourdough starter is just one of many you might choose to follow. Sourdough baking is as much art as science.
Just reduce the initial rising time to 4-5 hours if you use commercial yeast.