Your Service and Support Coverage - https://selfsolve.apple.com/agreementWarrantyDynamic.do - "Review your Apple warranty status and eligibility for support and extended coverage." Requires a hardware serial number.
I'll let you search the warranty information but my memory is you get the warranty from the date of your original purchase unless there's less than 90 days left of it in which case you get 90 days.
'For devices replaced during the original warranty period the new warranty is 90 days or the remainder of the original warranty, whichever is longer.'