Tell us within 48 hours of delivery and send photos. That is so we can raise it with the courier while the claim is still live, and the sooner we know the more we can do.
Your 30 days are not affected either way. If you get in touch after 48 hours it is still a return, and it is still ours to put right.
One thing that helps everyone: if the box itself looks damaged when the courier hands it over, do not accept the delivery.