Sid,
it would be better to get an earlier surgery - but I believe that the most important thing is to get the surgery right - with the best surgical team available. Make sure that the doctor and whoever deals with the doctor's schedule (a nurse or administrator - I don't know how it works in India) knows that you would like the surgery earlier if a slot opens up for it. Be really nice to that person!

If you have to wait a month, concentrate on great nutrition and more calories for your dad, so he will be in the best possible shape for the treatment. Remember to take care of yourself, too - it is not easy being the care giver, either.
Maria