Register with your serial number and purchase details. There is no cutoff.
Register on the Singapore store with your serial number, purchase date, purchase channel, and either your baby's estimated due date or birthday. A confirmation email is sent automatically once your registration is checked.
Registration is required to make a warranty claim later, so it is worth doing as soon as you can.
You will see a prompt to register within 7 days. That is an encouragement to act, not a deadline: registering later than 7 days is accepted in full and your warranty stays valid.