I want to use 110,000 miles to get my wife and me from Chicago O'Hare to Paris and return to O'hare from Zurich. I am willing to book 331 days in advance. Do I need to call at midnight CST or is it Hawaii time? Can I book the outbound trip and leave the return open so I can call in 10 days later to get the free seats on a United Flight operated by Swiss Air?

Thanks