Hi @Lolip92, though I don't work for China Post but I am someone who sent parcels to China from the UK several times this year, so perhaps I can show you a few of my timeline for your reference.

With Parcelforce Priority which promised to deliver 3-8 days, all 3 of my timeline vary from 6-8 weeks;
With the Royal Mails international track and signed, the mails I sent 7 weeks ago has just arrived in Shanghai, and still waiting in the queue of going out of Shanghai - I am anticipating 12-15 weeks for them now, as I see someone sent the mail from UK on 2nd April arrived at Shanghai on 2nd June is still in the queue now.

The zero covid policy has largely delay international deliveries to China Mainland. Even before the lockdown of Shanghai Apr-May, it look my parcel (with Royal Mail Int. Track and Sign) 1 month to arrive rather than 5-7days, and it was back in Feb. With Shanghai locking down for 2 month, everything will just delay by another 2 months, especially when Royal Mail just send everything to Shanghai (or Beijing, which is currently under lockdown) rather than other cities.

I just phoned China Post Shanghai yesterday and they recovered 95% of their pre lockdown delivery capability, and looking to go >100% next month; meanwhile the no. of cargo flights is 5x (15 vs. 3/week during lock down) between LHR and PVG now (you can check that on flightaware), so hopefully yours will just take 6-8 weeks rather than 12-15 weeks.

I hope the info. helps!