Microwaves vary in strength...and the thickness you sprinkle the cheese will vary the time also. Ours goes on a piece of deli paper (cling film not recommended) and 90 seconds cooking time. You want it to brown slightly or it doesn't crisp up. You have about 2 seconds when it comes out to shape it if you want. As they're done, I stack the pieces of deli paper up, keeping them nice and neat which reduces breakage. I forget who shared this info, but it was on this site. I've been popping them on caesar salads for garnish now because they're so easy. I will never make them in the oven again.
Also, has anyone noticed how quickly and easily the microwave clarifies butter?