AHow long after I open a tub of butter cream icing will it last?
It should have an expiration date printed on the label. It's usually a few months away from the time it's purchased.
Take it and put it in containers in your freezer. I freeze my butter cream icing all of the time when I make too much and have some left over. I just take it out of the freezer and let it sit out and it thaws pretty quickly. You did say butter cream not bettercreme, right? If it is bettercreme I have no experience with that.
AThe expiration date is in november will it still be good by thin if I don't freeze it?
It's fine at room temperature — best if stored between 70 - 75 degrees F.