I have used RTK a few times. Both times that I included butter, I used less than called for, and as soon as the RTK were out of the fridge and reached room temp., they softened and fell apart. Without butter, temp. doesn't matter. They hardened solid, but are still delicious -- it's cereal and marshmallows!
I will never use butter again; I've learned my lesson, only cereal and marshmallows.