I'm not sure that I would leave it on for two days straight, mainly because it would be completely unattended for at times, but really there is no threat structurally. It's mostly brass with a bit of teflon inside. The T-stat and P-stat life will be shortened because they'll be cycling more often. These always die eventually, though, and the P-stat is a snap to replace. The T-stat, depending on the machine, may be a little more interesting.
Get an appliance timer. I use one just to make sure it shuts off in case I forget.
- -Barrett