here is the link to my blog for both pondi and kodai. For kodaikanal two days are more than enough and a little suggestion don't take taxi if you really wish to enjoy that place and if you can walk. Walk to all the view points as all of them are on one road only. You'll see a kodai like never before. Then keep your remaining days for pondi as there are places where you will wish to go back again and again in pondi and do visit aurovile.
Hope it will help.
You can cover mahabalipuram and pondi in two days. if you are in chennai you can start your trip by visiting mahabalipuram first( shore temple) from there only you can take bus or cab to Pondicherry which will take 3 hrs.