There is currently an issue on SFTP Gateway related to timestamps. When viewing your files in an SFTP client, the timestamps show the current date and time, which continuously update to the current time. Files uploaded via SFTP Gateway show normal timestamps.
This issue is scheduled to be fixed in an upcoming version (3.3.1) of SFTP Gateway.
The cause of the timestamp issue
SFTP Gateway sets the timestamp on a custom metadata property, which it uses to determine the last modified date. However, existing S3 files, or files uploaded by other means, will not have this custom metadata property. SFTP Gateway will not be aware of the last modified date, and will fall back to displaying the current date and time.
We have filed an internal bug ticket for this, and plan to implement a fix that falls back to reading the S3 object's native last modified date.