Best way to make multiple countdown timers

with
cells B2 C2 D2 formated as custom Format pattern
00":"00":"00

Option Explicit
Dim iTimer As Date
Dim zTimer As Date
Dim xCount As Long
Dim iCount As Long
Dim xCell As Range
Dim eTime
Sub start_timers()
    With ThisWorkbook.Sheets(1)
        .Range("B2") = 5
        .Range("C2") = 10
        .Range("D2") = 150
        .Range("E2") = ""
        .Range("A2") = "Started"
    End With
    MasterTimer
End Sub
Sub MasterTimer()

    If ThisWorkbook.Sheets(1).Range("B2") > 4 Then
        xCount = 5
        Set xCell = ThisWorkbook.Sheets(1).Range("B2")
        eTime = TimeValue("00:00:05")
        iCount = 1
        UpdateiTimer
        STimer
    ElseIf ThisWorkbook.Sheets(1).Range("C2") > 4 Then
        xCount = 10
        iCount = 1
        Set xCell = ThisWorkbook.Sheets(1).Range("c2")
        eTime = TimeValue("00:00:10")
        UpdateiTimer
        STimer
    ElseIf ThisWorkbook.Sheets(1).Range("D2") > 4 Then
        xCount = 150
        iCount = 3
        Set xCell = ThisWorkbook.Sheets(1).Range("d2")
        eTime = TimeValue("00:00:50")
        UpdateiTimer
        STimer
    Else
        KillTimers
    End If
End Sub
Sub UpdateiTimer()
    xCell = xCount
    iTimer = Now + TimeValue("00:00:01")
    xCount = xCount - iCount
    Application.OnTime iTimer, "UpdateiTimer"
End Sub
Sub STimer()
    zTimer = Now + eTime
    Application.OnTime zTimer, "StopTimers"
End Sub
Sub StopTimers()
    On Error Resume Next
    Application.OnTime iTimer, "UpdateiTimer", , False
    Application.OnTime zTimer, "STimer", , False
    MasterTimer
End Sub
Sub KillTimers()
    On Error Resume Next
    Set xCell = Nothing
     Application.OnTime iTimer, "UpdateiTimer", , False
    Application.OnTime zTimer, "STimer", , False
    ThisWorkbook.Sheets(1).Range("E2") = "Stopped"
    ThisWorkbook.Sheets(1).Range("A2") = ""
End Sub