Does it have to be on all of the time or can you turn on when wishing to use? How long does it take for the water to heat once turned on?

Hello Brenda, hot tubs do stay on or "ready" all of the time. The pump has to turn on a couple of times per day in order to filter the water and the hot tub will also automatically maintain the set temperature that you leave it at; for example, perhaps 102 degrees Fahrenheit. The idea is that you can spontaneously decide to take a hot tub, lift the lid off and it is ready to go. Quality hot tubs like these have excellent insulation under the cabinet, as well as a thick insulating cover so that they are energy efficient.