I am Platinum Class now till November 2018. Two things if anyone can help. Is the complimentary upgrade to business class one way only? And when is it applied? At time of booking? Check in? Boarding? New to this loyalty program business so not sure. EI website and customer service not very good on this!

I've asked EI twice but they seem very reluctant to tell me anything other than to call once I've booked the flight. I'd rather know in advance what the story is if possible. Thanks in advance for any help.