Mahabalipuram is situated between Pondicherry and chennai. It's almost 1 hour from chennai and 1.5 from Pondicherry bu road. This is the reason most of the traveler take it as a 1 day destination.
We took a different turn and made it a budget private beach honeymoon destination for us.
We started from chennai early morning and reached joe beach resort. The resort has 2 swimming pools and a private beach. We did some early booking and got nice room for 2k per day. Don't forget to select sea access resort, not sea just viewing.
Obviously this is not a white sand luxury beach but most of the time there will be no one except you and your partner. It will provide you really good quality time and romantic moments, but remember to be 'civilised' and safe.