When used by Q in the past BDT stood for Bangladeshi Taka, the official currency for Bangladesh, as a heads up that the guy who attempted to set off a bomb on the NYC subway was from Bangladesh, and later confirmed. Since we are told to consider multiple meanings, it stands for British Daylight Time, and Behavior Driven Testing of Behavior Driven Development software. No time to dig further right now, as I'm a workfag.