To pass, the resumption of rate can be no more than 5 seconds. The COSC certificate is not a precise indicator of how well a watch will perform on the owner's wrist. Rather, the test results show how well a given movement performed over a given period of time under certain conditions. Several factors can affect the actual performance the owner observes. First, The COSC test is only an artificial approximation of actual use.
Movements can spend significant time in the vault.
When they do, they are usually disassembled, cleaned, re-assembled, oiled and regulated, then cased. This can certainly affect the movement's performance, yet re-testing is not required. Next, the watch may be affected by shipping in the distribution chain, where it might be exposed to shocks or extreme temperatures. Conditions at the dealer's shop also affect performance. If the watch sits unused for many months, if it sits under hot lights or in the window in the sun, if customers drop it while trying it on, this will affect how the watch performs on the owner's wrist.