Does anyone know if butter cream with egg whites can be left out at room temp?

yes it can

I was so confused.  I'm no gourmet but I was seriously thinking "I didnt even know there WERE egg whites in butter...."

AI believe she was just confused...wondering if butter itself is made with whites. Didn't read buttercream just read and thought butter

Hahaha,  I was thinking the same thing as kimmisue2009! But actually I've always had that nagging little doubt about meringue buttercreams - it's good to have an answer. Thanks, as always, -K8memphis!

Kimmisue, LOL too funny.. 

Margaret Braun says several days at a cool room temp. I accidently left some leftover smbc out for a couple weeks and I'm not suggesting that anyone leave theirs out for several weeks but I'm just saying it never turned and I was quite surprised actually.-- it still smelled as lovely as when I first made it. I discarded it and did not use it but it's sturdier than it seems.

You're very welcome, Marianna,

Thank you!