Did a refund back in April. Took them 7 days since acknowledgment of reciept to credit the cash back in my account. They charged me about 30 USD per ticket.
You need to contact the call center and cancel the tickets. After they confirm the cancellation they will provide you with new ticket numbers that reflect the cancellation.
Go to emirates.com/ae (it has to be this site, and not your local one).
Click help center -> contact us -> ask us -> topic:cancellations and changes -> Refunds
Fill out the form. Each individual/ticket gets a seperate form even if they are all on the same itinerary. Once forms submitted a representitive will email you acknowledgment of reciept. Usually within 24 hours.
As for the time limit, I don't believe there should be but, depends on the ticket restrictions and when you cancelled (eg: before departure or after departure.)
If you have a reference number the call center can pull up the ticket numbers for you and provide all the information after you supply them with confirmation of who you are over the phone. (e-mail, birthdate, etc.)
Hope it works out for you.
KU104