We want to see Milford sound traveling from Christchurch and returning the same day by air.Please advise.
Wow! You are going to need a healthy budget with this one!!
The most convenient way would be to use a Christchurch based operator such as https://christchurchhelicopters.co.nz alternatively you could take a domestic flight from CHC to Queenstown and then use a Queenstown operator such as Air Milford or Glacier Southern Lakes Helicopters before flying back to Christchurch. Just bear in mind with the latter option as well as requiring all of the weather gods working in your favour, you need your domestic flights to be on time. If your CHC to Qtn domestic flight is late and you miss your flight to Milford, you will likely be charged as a "no show".
This is not really practical.
If you wanted to take a cruise on Milford Sound you would need to request a pilot who has a rating for landing at Milford, as this requires special certification.
I suspect this will end up in the "too hard" basket, but good luck anyway.