23a60e63__Core_API___endpoint_reference__description
[field] client_mtime [description] 
For files, this is the modification time set by the desktop client when the file was added to Dropbox, in the standard date format. Since this time is not verified (the Dropbox server stores whatever the desktop client sends up), this should only be used for display purposes (such as sorting) and not, for example, to determine if a file has changed or not.
Dropbox - Core API - endpoint reference
description