It will be the same morning that you get so excited that you pee your pants. LOL I agree with dun chick but it depends on a lot of things..breed of chickens, time of year , feed, etc. I'm still waiting on my first egg too. Good Luck
If the weather is warm, probably when your hen(s) is/are 6 months old. Then, they are LITTLE eggs. But, they get bigger.
You DO celebrate, like when you child starts walking. Then, it's less exciting, like when your 3 rd child starts walking, and you forget to take out the camera, and when they're 21 they rag you about it.....................sorry....stream of consciousness took over.
I'm no expert, but myy Easter Egger started laying about a month and a half later than my RI Reds and Silkie. I got them all at the same time. The RI Reds and Silkie started at about 5 mos, the Easter Egger about 6.