$yesterday = [DateTime]::Today.AddDays(-1).ToString("M/dd/yyyy")
# OR I have to use ToString("MM/dd/yyyy") for months 10-12, but I need both formats to work.
#delete the temporary file
del .FTPfiles.txt
# Load WinSCP .NET assembly
Add-Type -Path "C:Program Files (x86)WinSCPWinSCPnet.dll"

# Setup session options
$sessionOptions = New-Object WinSCP.SessionOptions -Property @{
    Protocol = [WinSCP.Protocol]::Ftp
    HostName = "server.com"
    UserName = "joe"
    Password = "smith"
}

$session = New-Object WinSCP.Session

    try
    {
        # Connect
        $session.Open($sessionOptions)

        $directory = $session.ListDirectory("/Folder")

        foreach ($fileInfo in $directory.Files)
        {
            Write-Output ("{1} {0}" -f
                $fileInfo.Name, $fileInfo.LastWriteTime) >> FTPfiles.txt
        }
        $fileList = get-content .FTPfiles.txt | findstr $yesterday
        $stripped = $fileList -creplace '^.*Z12', 'Z12'


        # Download files
        $remotePath = "/Folder/"
        $transferOptions = New-Object WinSCP.TransferOptions
        $transferOptions.TransferMode = [WinSCP.TransferMode]::Binary

        $lines = $stripped

        foreach ($line in $lines)
        {
            Write-Host ("Downloading {0} ..." -f $line)
            $session.GetFiles($remotePath+$line, "C:Downloads").Check()
        }

    }


catch [Exception]
{
    Write-Host ("Error: {0}" -f $_.Exception.Message)
    exit 1
}
finally
{
    # Disconnect, clean up
    $session.Dispose()
}

FROM:
3/14/2017 2:04:00 AM Z1234_20170314050001_1.zip
3/14/2017 3:04:00 AM Z1234_20170315060002_1.zip
3/14/2017 4:04:00 AM Z1234_20170316070001_1.zip
3/14/2017 5:04:00 AM Z1234_20170317080001_1.zip

TO:
Z1234_20170314050001_1.zip
Z1234_20170315060002_1.zip
Z1234_20170316070001_1.zip
Z1234_20170317080001_1.zip