Updating from master file to read-only slave file

Hi! I'm working on a problem, which included two files: a master excel file and a slave read-only excel file. Both are with macro's.

The first file is the so-called master file. This file is open and is available for reading and writing.

The second file is the so-called slave file. This file is open and is read-only. The file is essentally a copy of the master file. Its cells contains references to the master file - like: ='[test-from.xlsm]Sheet1'!A2.

Both are on a server and the files are normally not opened on the same computer.

What a macro needs to do at the master file, is to save every 30 seconds, since it has been opened. I've tried doing that using this code:

Private Sub Auto_Open()

    'call all subs to start automatically
    Call StartTimer

End Sub

===

Sub Save_Timer()
    
    'TODO make if-statement to only save when workbook has changed

    ActiveWorkbook.Save
    'save ActiveWorkbook
   
    Application.OnTime Now() + TimeValue("00:00:30"), "Save_Timer"
    'starts timer to run for 30 seconds and starts Save_Timer
   
End Sub

What a second module needs to do at the slave file, is to update every reference (in essence recalculating?) and save afterwards every 15 seconds.

The code I've made so far:

Private Sub Auto_Open()

    'call all subs to start automatically
    Call Update_Links
    
End Sub

Sub Update_Links()
    
    'TODO make if-statement to only save when workbook has changed

    Application.CalculateFull
    'update all links

    ActiveWorkbook.Save
    'save ActiveWorkbook
   
    Application.OnTime Now() + TimeValue("00:00:15"), "Save_Timer"
    'starts timer to run for 15 seconds and starts Save_Timer
   
End Sub

How simple this might seem, it does not work. Anyone in to help a lost Excel user?