Hi Becky, many entirely naturally leavened (no added yeast) sourdough bread recipes allow for such an extended fermentation time. Often fermentation can be extended by refrigeration (as in our No Knead Sourdough Bread recipe), and some recipes with a very small amount of sourdough discard can even ferment at room temperature for 12 hours (as in our Pain de Campagne recipe). I'm not sure of the exact requirements to make sourdough bread suitable for your dietary needs, but you should certainly have lots of options. 

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