function Get-NtpTime {
# A function that sends UDP packets to NTP server
# via IPv4 or IPv6  to obtain the precise time.
#
# return: datetime (based local timezone) 
#         $null (no server or something went wrong)

    param([string]$NtpServer)

    try {
        # NTP packet (48 bytes)
        $ntpData = New-Object byte[] 48
        $ntpData[0] = 0x1B

        # Send to ntp server via 123/UDP
        $addresses = [System.Net.Dns]::GetHostAddresses($NtpServer)
        $udpClient = $null
        foreach ($addr in $addresses) {
            try {
                $udpClient = New-Object System.Net.Sockets.UdpClient($addr.AddressFamily)
                $endpoint = New-Object System.Net.IPEndPoint($addr, 123)
                $udpClient.Connect($endpoint)
                # Received a response
                [void]$udpClient.Send($ntpData, $ntpData.Length)
                $udpClient.Client.ReceiveTimeout = 1500
                $response = $udpClient.Receive([ref]$endpoint)
                if ($response) {
                  $udpClient.Close()
                  break
                }
            } catch {
                $udpClient.Close()
                $udpClient = $null
            }
        }
        if (-not $udpClient) { return $null }
        # NTP timestamps are stored in bytes 40-47 (based on January 1, 1900)
        $intPart  = [BitConverter]::ToUInt32(($response[43..40]), 0)
        $fracPart = [BitConverter]::ToUInt32(($response[47..44]), 0)
        $ms = ($fracPart * 1000) / 0x100000000
        $secondsSince1900 = $intPart
        $unixEpochOffset = 2208988800
        $unixSeconds = $secondsSince1900 - $unixEpochOffset
        $dateTime = (Get-Date "1970-01-01T00:00:00Z").AddSeconds($unixSeconds).AddMilliseconds($ms)
        return $dateTime.ToLocalTime()
    }
    catch {
        return $null
    }
}
# End of function Get-NtpTime

$vmname = "###YOUR VM NAME###"
$password = ConvertTo-SecureString "###USERS PASSWORD###" -AsPlainText -Force
$username = "###COMPUTERNAME(or DOMAIN)\USERNAME###"
$cred = New-Object System.Management.Automation.PSCredential($username , $password)
$ntpserver = "ntp.nict.jp"

# Check Hyper-V module
Import-Module Hyper-V -ErrorAction SilentlyContinue
if (!(Get-Command Get-VM -ErrorAction SilentlyContinue)) {
  return "Error: no hyper-v role or hyper-v cmdlet."
}

# Check VM status is running
$vmstatus = Get-VM -Name $vmname -ErrorAction SilentlyContinue
if ($vmstatus -eq $null) {
  return "Error: no such vm."
} elseif ($vmstatus.State -ne "Running") {
  return 0	# vm state not running
}

$baseTime = Get-NtpTime -NtpServer $ntpserver
if ($basetime) {
  # Write-Host "$($basetime) is get from $($ntpserver)"
} else {
  $basetime = Get-Date
  # Write-Host "$($basetime) is get from local pc time"
}


$vmTime = Invoke-Command -VMName $vmname -ScriptBlock {Get-Date} -Credential $cred -ErrorAction SilentlyContinue
if ($vmTime) {
  $diff = $baseTime - $vmTime
  return [int][Math]::Abs($diff.TotalSeconds)
} else {
  retnrn "Error: could not get time from vm."
}