thusly, as I understand it:
You use it to undo the last 24 hours.
At some random time, if you
use it a second time, it puts time back the way it was.
I think if someone ELSE uses it after your first time, since it's THEIR first time, it has no effect on what YOU did.
Not sure if that erases what would happen if you got it back and tried a second turn, though.