When to expect eggs
Anywhere from 18 to 24 weeks. The average being 18-19 weeks.
There are a lot of different factors that determine when a pullet starts to lay. Heredity is a big one and that should be in your favor with barred rocks. Day length, days getting longer or shorter, weather, how you feed them, and just whether a pullet wants to be a pain in the rear or not all factor in, some more important than others. How old they are right now can play a part. If they hit five months next spring when days are getting longer they will lay sooner rather than later. If they are already there, it could happen any time but who knows.
There are some clues that they might be getting ready to lay. CT hit a few of them. Most pullets’ wattles and combs turn bright red when they are getting ready to lay, but some chickens can change comb and wattle color intensity during the day for other reasons. Still it’s a good clue. Often when they reach sexual maturity pullets will start squatting for you or a rooster. But I’ve seen a 13 week old do that and she was two months away from laying. And they don’t always squat. It’s pretty common for a pullet to start looking for a safe place to lay about a week before they start to lay, but not all do that. A pullet that is laying or about to lay will have a big soft moist vent. One not close to laying will have a small hard dry vent. The distance between the pelvic bones is another clue, more width means more ready to lay.
These are all clues and if you see any of them that is a good sign. But they are just clues, they are not guarantees. It can get pretty frustrating at times. I wish you luck!
I've detailed my Barred Rock's 1st egg laying on http://www.backyardchickens.com/t/818035/if-you-see-a-hen-panting-and-looking-restless-give-her-a-nest-box#post_11992134
She laid her first at 20 weeks, after over 2 weeks of squatting. You can see videos of her on the thread.