You would have to write that.

I’ve never programmed in PowerShell or .NET. Does the WinSCP .NET assembly you refer to already exist, or is it something I'd have to write? If I have to write it, that’s a show stopper. Too much on my plate & too little time. Please advise.

WinSCP GUI synchronization indeed uses timestamps (or sizes) to find the modified files. It cannot use the Archive bit. Though it's easy to write a script for that, with use of WinSCP .NET assembly and e.g. a PowerShell script.

Yes, WinSCP can synchronize recursivelly.

We’re trying to determine whether we can use WinSCP to publish daily updates to our Web site.

Currently we use a custom FTP client, but it looks like we’ll have to upgrade to a more secure protocol. I see WinSCP offers secure FTP, but I have some additional questions:

Question 1: How does WinSCP determine “new and changed” files? Does it simply use the date time stamp? It seems to use the date time stamp when it “synchronizes” but that is painfully slow for our Web site, which has over 70,000 files. The first time we synchronized the Web site with our local copy, it took over 30 hours. Does WinSCP have a faster option, such as just examining the Windows archive bit (then clearing it after the file is uploaded)? This is the technique our custom FTP client uses: When it scans the entire local directory tree for files with the archive bit set, our custom client can detect and transfer a single new/changed HTML file in under 30 seconds.

Question 2: Can WinSCP transfer all “new and changed” files in a folder and all its subfolders?