As to once the blood vessel is blocked, symptoms come on immediately as the brain does not tolerate lack of blood flow to deliver its nutrients and oxygen. If, alternatively, the vessel leaks, those symptoms intensify over time, usually starting with an intense/sudden/severe headache, and symptoms can further develop or progress as the bleeding into the closed-space of the skull continues, depending upon where the event is taking place.
If in doubt, call 911. Time is brain.
Donald W. Alves, MD, MS, FACEP