Why 6months - From ASR pov

In normal pregnancy itself, people give extra care and nurture the woman with caution. This is Anjali we are talking. She is disabled, emotionally weak and most of all only person left for Arnav in his family. She needs support from both her husband and her family. What happens if Shyam leaves Anjali at this point? Its fatal!! For her and for the baby too...

ASR must have thought let her deliver the baby safely then throw Shyam out. As both Shyam and Khushi love each other, they will marry after 6 month period anyway. Now, Shyam can be kept under control or at least force him to 'fake' his responsibility for his Di. If he had left Shyam and Khushi roaming freely, there is a risk Shyam might not be available to Anjali when in need. He knows how stressful she gets when she don't see Shyam.

6 month is not only works for him, works for Khushi also, she can go and marry Shyam later.