You can use WinSCP .NET assembly from a PowerShell script.
Before posting, please read how to report bug or request support effectively.
Bug reports without an attached log file are usually useless.
So you want only to check that the remote file timestamps have changed (or that they all are newer than a certain time)? You do not need to download them?
That's very vague question. Where do you want to "extract" the timestamp to? What are you going to do with the timestamp?
Did you consider using synchronization?
Or downloading recent files only?
https://winscp.net/eng/docs/script_download_most_recent_file ("Alternatives" section)