Final answer:
The Bon Marché in Paris experienced massive growth by the 1860s but the provided information does not include data on when the second store opened.
Step-by-step explanation:
The information provided does not specify the exact month and year that the second store was opened, as it focuses on the historic development of the first real department store, the Bon Marché in Paris. The Bon Marché was a trailblazer in the department store industry, starting in the 1840s and going through several expansions to become a significant location in Paris.
The details provided give a rich history of the Bon Marché's rise to prominence, including its influence on consumer culture by participating in the birth of the seaside holiday in the 1860s, attracting massive numbers of clients during its sales, and making the department store a tourist destination comparable to that of the Arc de Triomphe.
However, to answer your question about when the second store was opened, additional specific historical data related to the store's expansion would be necessary, as the provided information does not contain those particulars.