Not sure if it's still the case, but the "Express Post Guarantee" was not honoured during the height of the pandemic.
Thing could be 3 weeks late and there was no recourse.
edit (yep):
22 September 2021
Express Post remains our fastest postal service, but our next-business-day guarantee is currently suspended.
This change is necessary due to:
COVID-19 health and safety regulations applying to workplaces
fewer passenger flights (which we usually rely upon to carry many of our parcels)
ongoing COVID-19 disruptions
We’ll reinstate our next-business-day guarantee as soon as we can.