Excluding weekends from Gantt Chart

Hi,

I have posted something similar about this in the past and the formula someone gave me worked wonderfully. However, only I new how to work the chart in the office so it wasn't practical. I would like to do the same with this gantt chart so they don't have to keep amending the timeline dates every time they put together a programme.

Basically we would like to exclude Saturdays and Sundays as working days but be able to add them in when and as we need them. On the last chart I could type a w onto the Saturday or Sunday I wanted to show as a working day and it highlighted that day. I'm hoping something similar is possible with this chart but I can't figure out how to tailor the formula I was given to suit the attached excel chart.

Can anyone help me please?