Update time automatically in Excel

Enter the below code in "ThisWorkbook"

Option Explicit

Private Sub Workbook_Open()
Flag = True
RunWhen = Now + TimeSerial(0, 0, 1)
Application.OnTime RunWhen, "UpdateClock"
End Sub

Private Sub Workbook_BeforeClose(Cancel As Boolean)
Flag = False
Call StopClock
End Sub

Enter the below code in "Module 1"

Option Explicit

Public Flag As Boolean
Public RunWhen As Double

Sub UpdateClock()
If Flag = True Then
' *** Change Sheet name and Range reference to suit ***
Worksheets("Sheet1").Range("A1").Calculate
RunWhen = RunWhen + TimeSerial(0, 0, 1)
Application.OnTime RunWhen, "UpdateClock"
End If
End Sub

Sub StopClock()
Application.OnTime EarliestTime:=RunWhen, Procedure:="UpdateClock", Schedule:=False
End Sub


Source: http://www.mrexcel.com/forum/showthread.php?t=31483&page=2