I've noticed a lot of planets that are made with templates (such as the terrestrial, lunar, martian template and others) always have a rotational period.
But I noticed that all planets made from the blank template don't have a rotational period.
I use the blank template a lot for my planets and I would like to know if there's a way to set a rotational period to a planet.
i think you mean the "default" rotation period that is displayed on the site and when you first place a planet in the system editor...
you can change that in XML, it's located somewhere near the top if i remember correctly, however it's in some super weird unit that i have no idea how to convert into any standard format