Some Amazon sellers sometimes ask transit time of delivery. 
Here we share the general transit time of cargo to different countries.

OCEAN SHIPMENTS
1,Cargo to USA.
Most of the cargo to USA will go to LA first, the city in the west coast of USA.
We usually load cargo at Ningbo and Shenzhen port.
In Ningbo, we have vessel from carrier MATSON who has fastest vessel in the market, 12 days from Ningbo to LA.
Other carriers around 14~16 days.
In Shenzhen, we have vessel from carrier ZIM who has fastest vessel which also 12 days transit time.
And other carriers around 14~16 days.
Vessels from MATSON/ZIM not only have fastest transit time in market, containers also can be discharged quickly, that's why they're expensive. TIME IS MONEY.
Cargo from China(most ports) to middle/east USA will take about 20~30 days.

2, Cargo to EU/UK
No matter cargo departure from which city in China, transit time all about 30 days. EU and UK are much further.

When cargo arrives destination port, it will take about 7 days to finish import declaration and devaning. Then we can book a slot and deliver to Amazon warehouse.
As we all know that COVID-19 messes up global logistics, currently can't guarantee delivery will on time. Currently UK. EU, USA are facing port congestion. Lots of container vessels are waiting for discharging.
If your cargo is delayed, please be patient, your forwarder will try his best but there's something beyond forwarder's power.

AIR shipments.
If you cargo is loaded on DIRECT FLIGHT, then cargo will be delivered to destination airport within 24 hours. Then finish import declaration and delivery
If loaded on TRANSIT FLIGHT, then you need to check with your forwarder case by case.

Hope this can hlep you.