With regard to onset of lay and different breeds there are so many variables it is very difficult to predict.
As a general rule, hybrids will come into lay earlier than pure breeds, light pure breeds before heavy breeds ..ie faverolles, cochins and brahmas which generally need a bit more time to mature.
Onset of lay is then determined by hormones, and the hormones that trigger this process are influenced mainly by the maturity of the birds and light..so if a bird is the right age for lay, but the days are shorter then onset of lay will likely be delayed till next February.
Physical signs of onset of lay are reddened face furniture, a gap between the bones on other side of the vent develops, in a pullet these bones are soft. pliable and closer together. The hen look overall a bit wider they become restlessness due to hormone surge, they can go off their feed for a little while and generally act a bit "fidgety".
Chicks hatched early..Feb/March usually come into lay late summer/ early autumn, later hatches often leave it until the next year.