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]