I am in the process of making SMBC and I have been beating it for like 20 minutes now and it's STILL not stiff. What am I doing wrong? I followed the recipe just like it said. Is this normal?

it sounds like you didn't heat up the egg whites and sugar long enough..that is the biggest key to making this..not sure what else could be the factor.

Beating with a hand mixer or electric mixer?
I don't agree that not heating the egg whites enough could be it. Maybe there is grease somewhere? Are you using real egg whites or pasteurized ones? Has it turned white at all? Sometimes it can take up to 20 minutes to get stiff peaks.

And are you saying the egg whites are not stiff or that you have added the butter and it is not turning into a thick frosting? If it is the later and it is a humid day and you have no AC on, it could take longer. You could also stick it in the fridge for 5-10 minutes and beat some more.

My dear husband is so great. He said "I wonder if it's because the air's not on" and soon as he cut it on it beat better. I didn't think not heating it enough could be it because I beat cold egg whites to stiff peaks all the time for different recipes. I was thinking maybe I heat it too much. Thanks for your help!