How long after accepting tribute can I attack an enemy civ?

I entered diplomatic relations with the English and demanded they provide tribute. It was easy, I have a pretty tight grip on the world, I just happened to be a number of turns away from being near their home to take it over.

But now I want to attack them and it says my reputation would be damaged if I attack them so soon. Not that I'm too worried about my reputation, but I might as well keep it if I can.

How long do I have to wait after accepting tribute until I can attack these fools who dared to settle in my world without sacrificing my spotless reputation?