Elizabeth I dies and James VI of Scotland accedes to the English throne. Elizabeth I died childless so was succeeded by her cousin, James VI of Scotland, who henceforth assumed the title of James I of England as well.
T minus zero means out of time.. This comes from a countdown convention used in by both the American military and NASA. Generally, it is used when counting down to a major event that will happen at a specific time. Mathematically, T is time, minus whatever amount of time is left until the event happens.
T-0 does not necessarily mean the exact time in this sequence when the liftoff happens, and can also stand for the time of main engine ignition, or anything similar, though usually close to the actual liftoff and rocket's clearing of the launch tower.