I am making a Chinese to go box cake and am going to make the noodles out of butter cream, I was going to do fondant but the stores here don't have an extruder and I don't have time to order one online. I don't have much time on the day of the part to pipe the noodles in the box, could they be done the day before and handle well? would I keep it out but covered in a cool place since the rest of the cake is fondant I cant put it in the fridge.

It will be fine. Buttercream doesn't melt that easily.

I second prterrell! Pipe away and good luck with the cake