DoEvents
WebAddress = "CONFIDENTIAL URL HERE" & WebID & "&t="

        Dim IE As Object

    Application.ScreenUpdating = False
    Application.Calculation = xlCalculationManual


  Set IE = CreateObject("InternetExplorer.Application")

  IE.Navigate WebAddress
  IE.Visible = True
  While IE.busy
    DoEvents  'wait until IE is done loading page.
  Wend

  Application.Wait (Now + TimeSerial(0, 0, 4))

  IE.Document.All("Response_123").Value = ThisWorkbook.Sheets("Sheet1").Range("B5")

Dim IE As Object

Sub demo()
    Application.ScreenUpdating = False

    Set IE = CreateObject("InternetExplorer.Application")
    IE.Visible = True
    IE.Navigate "C:UsersAdministratorDesktopsample.html"


    While IE.Busy
        DoEvents
    Wend

    wait 1
    IE.Document.getElementById("firstname").Value = ThisWorkbook.Sheets("Sheet1").Range("A1")
    wait 1
    IE.Document.getElementById("lastname").Value = ThisWorkbook.Sheets("Sheet1").Range("A2")
    wait 1
    IE.Document.getElementById("submit_btn").Click

    IE.Quit
    Set IE = Nothing

    Application.ScreenUpdating = True
End Sub

Private Sub wait(seconds As Long)
    Dim endTime As Date
    endTime = DateAdd("s", seconds, Now())
    Do While Now() < endTime
        DoEvents
    Loop

End Sub