User3, Welcome to OZgrid.
It seems to me you have the very answer you need with the example from Lacher's link.
Have you made any effort to adapt this to your situation?
See this thread: VBA Color Cells for Gannt Chart
Also: Gantt Charts - John Peltier
Search using these terms:
Excel Gannt Chart With Sliding Time Scale see thread: 60623
Custom Schedule - Gantt Chart see thread: 12824