Asuka and Nara Periods (538-794)
In my opinion, not much changed in terms of Japanese "art evolution" during these periods. However, the earliest Japanese sculptures of the Buddha are dated to back to the Asuka and Nara periods, which coincides with the introduction of Buddhism in the country.
Here's an interesting little tidbit that I found about Buddha ("the awakened"). His birth name was Siddhartha Gautama, and at age 30 he left a life of luxury and devoted himself to years of contemplation and self-denial. According to tradition, he finally reached enlightenment while sitting beneath a pipal tree (know known as the Bohdi tree) in India. Henceforth, known as Buddha, he spent his life teaching his disciples about his beliefs and the goal of achieving the enlightened state of Nirvana, which is the perfect peace of the state of mind that is free from craving, anger and other afflictive states. He died at age 80, possibly from food poisoning.