I'd give her a full week from the first day you noticed her sitting, to make sure she is "determined", as often first timers don't really know the ropes and give up after a bit. as long as she is trans like, has the growly broody cluck and looks determined, you can add eggs later. you can also look for a broody poop, which is much larger than normal, allowing them to get up once a day for food and pooping. it's fine if they are off the eggs for a half hour or so about once a day. if she gives up, you have about 12 hours to get those eggs in a incubator without loosing them all and expect the hatch time to be a bit delayed. if you already have the eggs, and they are fresh, you can just keep them at room temp, out of the sun for a few more days without effecting fertility much just to make sure she is for reals. then, at night, swap the golf balls for the eggs and go for it! good luck, it's so fun to watch a broody hen do their thing, the mothering of chicks is adorable.