I would bake in the microwave for about 2-3 minutes but check after about 1-1/2 minutes.
It also matters if you are cooking multiple muffins say in a casserole dish - they recommend 6 at a time.
Also a factor - high or low on your microwave.
Again, I'd check after 1-1/2 minutes and go from there. A toothpick you insert in the center of the muffin should come out clean for the muffin to be done.
Hope that helps!