The opening date comes from an article in the Hong Kong Daily Press, 1886-08-14, pg02, which reported the opening of the Bank's new building on that day. (Though to be 100% correct, the article notes that "although the Bank is being removed into it, the building is far from completed, and it will not be finished, at all events, within six months."
Other notes from the article:
15-19, Queen's Road Central.
Some notes I've found about this building:
1935. The 3rd Dec edition of the HK Telegraph reports that Marina House is complete:
"With every modern convenience and imposing in design, the new building next to the Hongkong Hotel in Queen's Road Central, to be called "Marina House", is now completed and will be ready for tenants to move in on January 1, 1936.
The building was completed in 1898, and was originally just known by its address: 2 Connaught Road
In 1939 it was sold to a new Japanese owner, and renamed: New Oriental Building
The club moved here from their previous building on Queen's Road.
Notes from Wikipedia:
The bank was named The Chartered Bank, until the friendly merger with The Standard Bank 1969.
I don't have an exact date for it's completion, but an article from the China Mail (1957-05-16, pg1) reports that the Governor, Sir Alexander Grantham, laid the foundation stone for the new bank building on that day. It was estimated that the building would be completed in 1959, and would then be the tallest building in the Colony at 244 feet from pavement to roof.
Views of Central from the harbour in the 1950s were dominated by the buildings of the HSBC Bank (on the right) and the Bank of China: