First heating is probably way too much. Haven't checked the wattage on my micro, but it's ancient so I doubt it's more than 700 watts. My first heating is a minute at the most. I use 6 or 7 drops stabilizer in 4 oz. It isn't absolutely necessary, I worked with it for over a year and learned very well how to not burn plastic.

But it can save you if you accidentally heat longer than you should or if a color heats up faster than you expect. Usually 1 min, 30 sec, 20 sec if it's fairly warm outside. This time of year with the cold, it's more like 1 min, 30 sec, 30 sec, 15-20 sec. Stirring between each interval of course. Usually I'll add my glitter before that last 15 sec. I usually work with 4 or 6 oz batches, but even 2 oz batches will get about the same treatment for heating.