<customUI xmlns="http://schemas.microsoft.com/office/2009/07/customui" onLoad="RibbonOnLoad">
  <ribbon>
    <tabs>
      <tab id="T1" label="MyTab" insertBeforeMso="TabHome">
        <group id="G1" label="buttons">
          <button id="G1B1" imageMso="NavDrillDown" label="Start" tag="btnStart" size="large" onAction="btnStart"/>
          <button id="G1B2" imageMso="CancelRequest" label="Stop" tag="btnStopTag" size="large" getEnabled="GetEnabledMacro" onAction="btnStop"/>
        </group>
      </tab>
    </tabs>
  </ribbon>
</customUI>

Option Explicit

Public myRib As IRibbonUI
Public myTag As String
Public btnStopPressed As Boolean

'ribbon
Sub RibbonOnLoad(ribbon As IRibbonUI)
    Set myRib = ribbon
End Sub

Sub GetEnabledMacro(control As IRibbonControl, ByRef Enabled)
    If myTag = "Enable" Then
        Enabled = True
    Else
        If control.Tag Like myTag Then
            Enabled = True
        Else
            Enabled = False
        End If
    End If
End Sub

Sub RefreshRibbon(Tag As String)
    myTag = Tag
    If myRib Is Nothing Then
        MsgBox "Error, Save/Restart your workbook"
    Else
        myRib.Invalidate
    End If
End Sub

'buttons
Sub btnStart(control As IRibbonControl)
    Call RefreshRibbon(Tag:="btnStopTag")
    Call StatusBarProgress
End Sub

Sub btnStop(control As IRibbonControl)
    btnStopPressed = True
    Call RefreshRibbon(Tag:="")
End Sub

'routine
Sub StatusBarProgress()
    Dim iTask As Long
    Dim TotalTasks As Long
    Dim secondsPerTask As Integer
    Dim TimeStart As Double

    secondsPerTask = 0.1
    TotalTasks = 3000
    TimeStart = Now

    For iTask = 1 To TotalTasks
        DoEvents
        If btnStopPressed Then GoTo myEnd

        Application.StatusBar = iTask & " of " & TotalTasks & " " & Format(iTask / TotalTasks, "0.0%") & _
        "   EndOn: " & Format(Now + (TotalTasks - iTask) * secondsPerTask / 86400, "YYYY-MM-DD hh:mm:ss") & _
        "   Remaining: " & Format(Now - TimeStart, "hh:mm:ss") & " of " & Format(TotalTasks * secondsPerTask / 86400, "hh:mm:ss")

    Next iTask

myEnd:
    Application.StatusBar = False
    btnStopPressed = False
    Call RefreshRibbon(Tag:="")
End Sub