%datatime% is not a supported macro. The adapter currently does only support %MessageID% and %SourceFileName%.

It's a small thing to add. Download the source code and open the Blogical.Adapters.Sftp.sln solution. In the Blogical.Shared.Adapters.Sftp project, open SftpTransmitProperties.cs, and go to line 340.
Update the ReplaceMacros to below (I haven't tested tihs code). This should give you two macros %DateTime% and %UniversalDateTime%.

Let me know how it works

private static string ReplaceMacros(IBaseMessage message, string uri)
{

if (uri.IndexOf("%MessageID%") > -1)
{
    Guid msgId = message.MessageID;

    uri = uri.Replace("%MessageID%", msgId.ToString());
}
if (uri.IndexOf("%SourceFileName%") > -1)
{
    string sourceFileName = string.Empty;
    try
    {
        string filePath = GetReceivedFileName(message);
        sourceFileName = Path.GetFileName(filePath);
    }
    catch 
    {
        throw new Exception("The %SourceFileName% macro can only be used with the " + Constants.SFTP_ADAPTER_PROPERTIES_NAMESPACE + " namespace.");
    }
    uri = uri.Replace("%SourceFileName%", sourceFileName);
}
if (uri.IndexOf("%DateTime%") > -1)
{
    string dateTime = DateTime.Now.ToString();

    uri = uri.Replace("%DateTime%", dateTime);
}
if (uri.IndexOf("%UniversalDateTime%") > -1)
{
    string dateTime = DateTime.Now.ToUniversalTime();

    uri = uri.Replace("%UniversalDateTime%", dateTime);
}

return uri;

}