Dear Akshay,
I have answered a similar question on Quora earlier; please refer to my answer to that question - link is given below. Then, you will get some idea on how a few hours change in birth time can change the horoscope and native’s life drastically.
So, 3–4 years is a huge time period. Any year can be best or worst depending on different smaller time frames within it due to difference in ownership of houses for planets according to ascendant; difference in karakatva because of degrees of planets and difference in placement of Gulika, Maandi, Bhrigu Bindu, etc.
Moreover, finding out the best time for child birth and deciding the best time to conceive a child, are both quite different. Because we also need to check the possibility of success in conceiving a child in this case. So, we also need to check the horoscopes of both the parents in this scenario and only then, we can find out best possible year/month to conceive.
So, if you are sincerely trying to find a best possible time for conceiving a child, then you can consult me. Check my profile message to get in touch with me!
You may also follow me on Twitter!