How long can a cake that is decorated in buttercream that is made with 1/2 butter, and 1/2 crisco, instead of all crisco be left out of the refrigerator and do you use butter with salt or without salt?

Some may disagree...but...I personally have had no problems leaving the buttercream out for several days, but it is always covered either in a cake container or with fondant, but it is still room temp. I use regular salted butter.

its to do with how much sugar you use as to whether or not it needs refridgerated i believe.
xx

Definitely up to 5 days

I've never had any trouble leaving buttercream icing out ( at room temp) on the cake or even if it's just in a tupperware. It can stay out for several days.