Downloading an image from the Internet with specific DateTime in the URL

I changed the DateTime conversion method, using TimeZoneInfo.ConvertTimeBySystemTimeZoneId, passing my Local TimeZone.Id and "Tokyo Standard Time" as parameters, to generate a DateTimeOffset that represents the current Tokyo DateTime.

Using a Timer, subtracting 4 seconds from the calculated DateTimeOffset (DateTimeOffset.AddSeconds(-4)), the Images are loaded correctly.

► Note that the System clock must be synchronized with a NTP Server. 4 seconds is a relatively loose gap, but an unsynched clock will of course compromise the result anyway.

EDIT:
Changed System.Windows.Forms.Timer to System.Timers.Timer, since what takes more time here is the image download.
Using BeginInvoke() to set the PictureBox.Image, which takes almost nothing, prevents the UI from stuttering when the Form is moved around.

Private tokyoTimer As System.Timers.Timer = Nothing
Private tokyoClient As WebClient

Private Sub btnStart_Click(sender As Object, e As EventArgs) Handles btnStart.Click
    tokyoTimer = New System.Timers.Timer() With {.Interval = 1000}
    tokyoClient = New WebClient()
    AddHandler tokyoTimer.Elapsed,
        Sub()
            Dim TokyoOffset = TimeZoneInfo.ConvertTimeBySystemTimeZoneId(Date.Now, TimeZoneInfo.Local.Id, "Tokyo Standard Time")
            Dim currentImage As String = TokyoOffset.AddSeconds(-4).ToString("yyyyMMdd/yyyyMMddHHmmss") & ".jma_s.gif"
            Try
                Dim data = tokyoClient.DownloadData(New Uri($"http://www.kmoni.bosai.go.jp/data/map_img/RealTimeImg/jma_s/{currentImage}"))
                BeginInvoke(New MethodInvoker(
                    Sub()
                        PictureBox1.Image?.Dispose()
                        PictureBox1.Image = Image.FromStream(New MemoryStream(data))
                    End Sub))
            Catch ex As Exception
                ' The exception hadling can be quite extensive here, since many factor can cause it: 
                ' No server response, no Internet connection, internal server (500+) faults etc.
                Console.WriteLine(ex.Message)
            End Try
        End Sub
    tokyoTimer.Enabled = True
End Sub

Private Sub btnStop_Click(sender As Object, e As EventArgs) Handles btnStop.Click
    tokyoTimer.Enabled = False
    tokyoTimer.Dispose()
    tokyoClient?.Dispose()
End Sub

An asynchronous version of the same procedure, all contained in a class object.
The TokyoImagesDownloader class exposes two public methods:

▶ StartDownload() expects as arguments:

1. The PicureBox control used to show the downloaded images
2. The interval, in seconds, between downloads.
3. A delay value, in seconds, to subtract to the current Tokyo Local Time, to prevent the Server from returning 404 - Not found because the requested image is not yet ready.

A StopWatch is used to synchronize the requested Interval between downloads, considering the time needed to download and show an image, so the clock shown in the Image itself should reflect the Interval requested.

▶ StopDownload() can be called at any time to stop the download of the images.

With:

StartDownload(PictureBox1, 1, 8)

the class is instructed to show the images in PictureBox1, download an image each second and delay the current Tokyo Time by 8 seconds.

Dim imageDonwloder As TokyoImagesDownloader = Nothing

Private Sub btnStart_Click(sender As Object, e As EventArgs) Handles btnStart.Click
    imageDonwloder = New TokyoImagesDownloader()
    imageDonwloder.StartDownload(PictureBox1, 1, 8)
End Sub

Private Sub btnStop_Click(sender As Object, e As EventArgs) Handles btnStop.Click
    imageDonwloder.StopDownload()
End Sub

Imports System.IO
Imports System.Net

Public Class TokyoImagesDownloader

    Private tokyoClient As WebClient
    Private cts As CancellationTokenSource = Nothing

    Public Sub StartDownload(canvas As PictureBox, intervalSeconds As Integer, serverTimeDelaySeconds As Integer)
        cts = New CancellationTokenSource()
        tokyoClient = New WebClient()
        Task.Run(Function() DownloadAsync(canvas, intervalSeconds, serverTimeDelaySeconds))
    End Sub

    Private Async Function DownloadAsync(canvas As PictureBox, intervalSeconds As Integer, serverTimeDelaySeconds As Integer) As Task
        Dim downloadTimeWatch As Stopwatch = New Stopwatch()
        downloadTimeWatch.Start()
        Do
            If cts.IsCancellationRequested Then Return
            Dim TokyoOffset = TimeZoneInfo.ConvertTimeBySystemTimeZoneId(Date.Now, TimeZoneInfo.Local.Id, "Tokyo Standard Time")
            Dim currentImage As String = TokyoOffset.AddSeconds(-serverTimeDelaySeconds).ToString("yyyyMMdd/yyyyMMddHHmmss")
            Dim url = New Uri($"http://www.kmoni.bosai.go.jp/data/map_img/RealTimeImg/jma_s/{currentImage}.jma_s.gif")
            Try
                Dim data = Await tokyoClient.DownloadDataTaskAsync(url)
                canvas.BeginInvoke(New MethodInvoker(
                    Sub()
                        canvas.Image?.Dispose()
                        canvas.Image = Image.FromStream(New MemoryStream(data))
                    End Sub))
                Await Task.Delay((intervalSeconds * 1000) - CInt(downloadTimeWatch.ElapsedMilliseconds))
                downloadTimeWatch.Restart()
            Catch wEx As WebException
                Console.WriteLine(wEx.Message)
            End Try
        Loop
    End Function

    Public Sub StopDownload()
        cts.Cancel()
        tokyoClient?.CancelAsync()
        tokyoClient?.Dispose()
        cts?.Dispose()
    End Sub
End Class