The ideal time for useage of a Terminator is 24hours which is in the instructions by Don. If you can't manage this he says at least 20 mins but I always say hes wrong and 1 hour is the minimum useage of the zapper. If you wear it for long periods of time especially asleep then soles of the feet are best to prevent burns from the electrodes.
I use the Terminator for at least 1 hour a day now but I've used it for years everyday. I completed the Bob Beck protocol of 180 hours on the SOTA machine in 3 weeks instead of messing around 2 hours a day for 3 months ;-) I didn't wear them together and you shouldn't expose the body to different electrical devices at the same time also you could damage some units. This would definately be a possibility if you use a Violet Ray and wear a zapper haha a zapper don't like 30,000 volts going up its butt and in the puny 555 chip :-)