when is the right time to conceive a new child, how to conceive boy or girl, how to conceive rich/beautiful/good child, how to avoid mentally retarded or otherwise disabled child ... 

In Hindu astrology days are calculated in slabs of 24 hours from start of menses of wife. 

The following chart is used to then plan conception of a good child. [Ref: Jataka Parijaatam III.18]

day Result
4 short lived boy
5 girl
6 son who will strengthen the whole family
7 childless girl
8 childless boy
9 beautiful girl
10 good son
11 shapeless girl
12 famous boy
13 sinful girl
14 well behaved, dutiful and charitably inclined son
15 well behaved, dutiful and charitable daughter
16 son who knows everything, highly learned