Correct guys!!

It is usually used when one someone is rushing or JUMPING THE GUN, which means taking action too soon. It comes from the days when we used horse-drawn carriages or rode horses and so literally had to hold the horses so they would wait patiently before starting off.

"Hang on! Hold your horses, I haven't even go inside the door yet, let me put my bag down and then you can tell me what happened!"

Hold your horses! We haven't won yet so don't get the champagne out just yet!