17.1.2(a) If the Damage is physical in nature, within seven (7) days of receipt of the Checked Baggage.

17.1.2(b) If the Damage consists of complete loss of the Checked Baggage, within twenty-one (21) days from the date on which the Baggage ought to have been delivered to you.

17.1.2(c)If the Damage consists of delay to the checked Baggage, within twenty-one (21) days from the date of the Baggage was place at your disposal.

17.1.3 If you do not notify us in writing within the timescales in Articles 17.1.2(a) to 17.1.2(c)above, and the Warsaw Convention or the Montreal Convention applies to your claim, no action shall lie against us save in the case of fraud on our part.

https://www.cathaypacific.com/conten...baggage-en.pdf

Not sure if damage to hard disks qualifies as physical damage or complete loss, but CX in giving 21 days is already the generous interpretation of their rules. Good luck on the insurance!