How Does A Syringe Driver Of Constant Morphine Hasten Demise?

My grandmother is soon to be put on a syringe driver of constant morphine to bring her death quicker to stop her from suffering any longer, how long does the procedure take at the time of administering to the time the body shuts down? She's been semicomatose for 5 days now, the doctor who initially examined her on arriving at the hospital didn't think she would make it through the night.