I had 15 sexlinks last year, and a few miscellaneous hens (EE, Jersey, silkie) and my average was 13-14 eggs per day. That takes into account through the winter, etc. Even with sexlinks (I had commercially bred ISA's) you are most likely not going to get an egg every day from every hen. They still fluctuate with the weather, sunshine, temperature, things going on around the environment. We had a coyote scare one day, in broad daylight...took one of the ISA's and I only got 6 eggs that day from the rest of the girls. So all things considered, you can easily plan on 12 eggs per day except perhaps in the darkest, coldest days of winter.
Also, my ISA's started laying around 16 weeks and all were laying by 20 weeks. This year I bought red sexlink chicks from Ideal to raise up for someone. They were 20 weeks old on Monday and not even one egg in sight yet. So even sexlinks are not created equal.