As Confucius was ignored by the rulers in his time, when did Confucius's ideas and philosophy actually start to become influential in China?
It is a mistake to say that Confucius was ignored during his lifetime or at any time thereafter, as this simply is not true. He had numerous disciples who called him "master philosopher king" (Kong Fuzi, hence "Confucius.") He was unable to gain a governmental position during his lifetime as he insisted on principle rather than expediency, but worked as an educator and political adviser throughout his lifetime and earned considerable respect as a result. His influence on his disciples was exceptionally profound; so much so that the influence of his teachings and those of his disciples was important in Chinese culture for almost two thousand years. His disciples compiled his teachings into the Analects which remain important in Chinese culture.
It is also a mistake to denominate Confucianism as an "official religion," as it is not a religion at all, nor is it even a philosophy. Chinese culture by its very nature is not overtly religious; and Confucius considered religious matters to be too abstract for humans to understand. He rather advocated efficiency in government and moral rectitude.
Because his principles prevented him from obtaining a government position, Confucius considered himself a failure, and only lived an additional five years; however during his life, he enjoyed considerable prestige as a teacher.
I would say that it took more than 200 years for Confucius's ideas to truly become very influential in China. Confucius died in 479 BCE. It was not until the 2nd century that his ideas came to have great influence. By that time Confucius's works were the texts that all men who wished to become government officials had to know. By the time of the Western Han Dynasty (starting in 208 BCE), Confucianism was the offical philosophy (one might call it an official religion) of the empire. This shows us that, by 280 years after Confucius died, his ideas were extremely influential.