The timing has everything to do with the Roman Empire and its all-pervasive political power over almost all of Europe, North Africa and what we call the Near East. It has nothing whatever to do with God. The development of Christianity was spurred, in part at least, by the fact that a whole lot of very disparate cultures were now more or less united under one banner, i.e. the war eagle and the fasces
of imperial Rome. Coincidentally, Judea was one of those outlying Roman territories and the creed of its population of Hebrews had evolved into a monotheistic belief, akin to an ancient Egyptian belief, which posited the coming of a Messiah who would bring the kingdom of Heaven down here to earth. Another coincidence -- one of the people to pick up on this whole notion of spreading the word of an obscure Rabbi from Nazareth beyond the borders of Judea happened to be a super-salesman. That was Saul of Tarsus, a Roman citizen of Jewish extraction whom we now call Saint Paul. The time and the place were ideal for a message of love, peace and redemption and Saul sold it well.
Please refer all other questions to Frank.