The short version: nine to fourteen days is normal, the pack is spent within two, and the solid does not mind.
A single phase-change pack in a thin-walled box holds below ten degrees for roughly one to two days at twenty-five degrees ambient and under a day at thirty-five. On a twelve-day lane the material is at ambient for most of the journey regardless of what was packed.
Reported ranges from Chinese origins to western Europe cluster around nine to fourteen days with tracking, with inland origins adding a domestic leg and coastal ones sometimes beating the range.
Phase-change pack hold times are a function of mass, latent heat and box insulation, and published figures for small parcels are on the order of a day or two.
Buy a data logger if the temperature history genuinely matters to you.
edited 12 Sept 2025 by ines_brandt — updated for the 2026 guidance change