People of Earth. I AM LRRR, RULER OF THE PLANET OMICRON PERSEI 8! We will raise your planet's temperature by one million degrees a day, for five days, unless we see McNeal at 9pm tomorrow - 8 central!

Pretty sure just one day would do it for us. Maybe it's Omicronian metric degrees and they're really precise?

With gravitational lensing, this is actually viable! Just send a signal at a gravity sink, and travel at sublight speeds to position yourself in a place where it will be redirected to eventually along a longer path, and you can intercept your own signal! You just have to be really, really lucky.

Assuming some pass through non-empty media, isn't it technically possible?