The soul does not enter our body. Amused? Now be serious. Be silent and think deeply for a while what is really meant by the soul or ātman. The ātman and the jivātman are not two different things. The ātman manifested in a jiva or living being is called jivātman. It is also essentially the same as the Paramātman. Brahman is also That. Bhagavān or God is an aspect of Brahman. These words have a little difference in exact connotations. But, in a simple way, all of them stand for the same thing. The difference lies in the angle from which we see the same Truth. The Truth is but one.
In colloquial terms a thing means something like brick, wood, stone, etc. Actually a thing is whatever we can think of. If we are able to conceive something mentally, it is called a thing. The thing which is eternal, which has neither birth nor death, which has no change, no modification, is the real and fundamental thing, out of which everything else comes. It is variously called Brahman, Ātman, Bhagavān, etc. It appears or manifests Itself as the universe with all its material things and living beings. You may describe it in so many ways, but all that we see in this universe are Its different manifestations only.
This is the central idea of the philosophical thoughts of our country. There is no question of a soul entering a body, because there is nothing but the soul. This table and everything else that we see are different forms of the soul, and we are also the soul. Sri Ramakrishna said: God is the only thing. In other words, all things are in reality God. And the soul is God. So, the body and mind of human beings are also different manifestations of the soul. The degree of manifestation is different in different things. It is the least in matter, more in living beings, even more in human beings, and the most in pure and selfless men and women. But it is there everywhere. So, the question of a soul entering a body at a particular time does not arise.