I think I see my confusion. In Session Properties, it says "Maximal interval between two consecutive outputs from WinSCP console session, before TimeoutException is thrown. The default is one minute." In SessionOptions Properties, it says "Server response timeout. Defaults to 15 seconds." I'm now using it in both Session and SessionOptions just in case.
I have updated documentation of
Session.Timeoutto make it clear, one should hardly ever want to set it.