Honest answer: international mail times depend more on the two postal systems involved and customs than on distance, so ranges are wide.
The variance comes from predictable places. Customs clearance at the destination can add days or weeks, especially for parcels with value. The destination's internal postal quality matters enormously; the same letter from one origin can reach one country in a week and a neighboring one in a month. Peak seasons around major holidays slow everything, and remote areas add final-mile days anywhere.
For planning, check the delivery estimates the origin postal service publishes per destination and service, then add a cushion for customs. If a date genuinely matters, like documents for a visa application, skip the post entirely and pay for an express courier with tracking. And always get tracking; the estimate matters less when you can see where the item actually is.