There's no specific formation time for "redwall limestone." This name likely refers to a specific geological formation, which is a layer of rock with unique characteristics. To answer when it formed, we need more information:

Please clarify what you mean by "redwall limestone":

* Are you referring to a specific geological formation with that name? If so, which one? There are several geological formations containing red limestone, each with its own formation period.

* Are you referring to a particular location? The formation time of limestone can vary greatly depending on the specific location.

* Are you referring to limestone with a specific red color? Limestone can be red for various reasons (iron oxides, specific minerals), and the timing of its formation can depend on these factors.

Once you provide more details, I can help determine the specific timeframe of its formation.