Help with the tic button, not the comand button

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This code works with comand buttons.
I have tried to do it with just buttons but can't get it to work.
When I click on a button it starts the timer, when I click on a different button it stops the running timer then starts the next timer.
I need it to work with the tic button not the comand button button.
Can someone tell me or help with rewriting the code Please?

Option Explicit
Dim StopTimer As Boolean
Private Sub CommandButton1_Click()
  'Start the timer
  Const Minutes = 480
  Dim EndTime As Double
  StopTimer = False
  Do
    If EndTime - Now < 0 Then
      EndTime = Now + TimeSerial(0, Minutes, 0)
    End If
    Range("G7") = EndTime - Now
    DoEvents
  Loop Until StopTimer
End Sub

Private Sub CommandButton3_Click()
  'Start the timer
  Const Minutes = 660
  Dim EndTime As Double
  StopTimer = False
  Do
    If EndTime - Now < 0 Then
      EndTime = Now + TimeSerial(0, Minutes, 0)
    End If
    Range("G10") = EndTime - Now
    DoEvents
  Loop Until StopTimer
End Sub

Private Sub CommandButton5_Click()
  'Start the timer
  Const Minutes = 840
  Dim EndTime As Double
  StopTimer = False
  Do
    If EndTime - Now < 0 Then
      EndTime = Now + TimeSerial(0, Minutes, 0)
    End If
    Range("G13") = EndTime - Now
    DoEvents
  Loop Until StopTimer
End Sub

Private Sub CommandButton7_Click()
  'Start the timer
  Const Minutes = 4200
  Dim EndTime As Double
  StopTimer = False
  Do
    If EndTime - Now < 0 Then
      EndTime = Now + TimeSerial(0, Minutes, 0)
    End If
    Range("G16") = EndTime - Now
    DoEvents
  Loop Until StopTimer
End Sub

 

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I am trying to get this code to work a tic button but can't get it work.
Help Please