1. Should be pretty close to the same, maybe add 2 seconds to the heat up time.
2. Just as long as its mixed I don't think it matters. I've never had to use the heat pads. Just nuking it and putting it in my crotch always worked perfect.
3. It gets fairly warm I would recommend having the pad on the outside. Putting the bottle in the crotch generally keeps the heat a lot more constant.
4. I've had it stuffed in my crotch for up to 2 hours and it was always good. Also remember if the temp gets a little low, rub your thumb against your pants and after the urine is placed in the colletion cup place your thumb on the temp strip for a few seconds. Get it to 98 or 99 then walk out of the room and hand it to the tech.