I can not say I have ever seen specific directions like temp & such for M&P bases. You can melt it in the microwave or in a double boiler. The key is not to over cook it.
I place some (2# or less) in a pyrex measuring cup & watch it melt in the microwave, I take mine out when there may still be very small unmelted pieces floating about. These will melt when you stir. If you did not over heat the base, if it is not bubbling, you may add the fragrance.
You will get familiar with your microwave & your base of choice. I find 1# melts in 50 seconds. 1/2# will melt in 30.
It is ready to pour right away, but it does not hurt to wait a few minutes. I think it is easier on your molds to let it cool a bit.
If you choose to something like oatmeal, poppyseeds or glitter, you will want to gently stir untill it has cooled enough that your additive will not sink to the bottom, unless that is the look you are going for.
After pouring I sugest misting the top of the still melted soap with rubbing alcohol, the alcohol will evaporate and leave you with a smooth surface. It will also pop any bubbles that have settled on the surface.