Are you expecting this information to be automatically available? Are you looking for info management advice? Might you be trying to decide whether to update or redefine a block?
As the other have stated, internal block time stamps are not a built-in capability. That said, if, looking forward, you consider this information important, you could add it to your block definitions either in attributes, as xdata, or in the block description. Manually updating that information might get tedious and error prone. Such capabilities could be automated via customization. If your blocks are drawings themselves, the time stamps are managed and available via the operating system as the file date information.
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