Question: How much time does it takes to heat the water
Answer: 6 minutes
Answer: If you forget to switch off the geyser then it automatically cuts off when a particular temperature is reached... But when after a long time the temperature goes down it will keep on switching on and off to maintain that temperature so you keep on adding to your electric meter reading.
If the tap is left open so naturally the hot water keeps flowing out and it being an instant geyser will keep on heating water that is flowing into it.
Means it will stay on and the electric meter will keep running.