To create a waterfall chart in Excel with time on the X-axis and the % reduction in defects on the Y-axis, you can follow these steps:

1. Enter your data into Excel, with columns for Initiative, % Improvement, and Implementation Date.
   
2. Select the data and insert a stacked bar chart.
   
3. Right-click on the chart, and select "Change Chart Type".
   
4. Select the "Waterfall" chart type.
   
5. In the "Design" tab under "Chart Layouts", choose a layout that includes a legend and axis titles.
   
6. Right-click on any of the bars in the chart and select "Format Data Series".
   
7. In the "Series Options" tab, choose a fill color for the bars.
   
8. In the "Gap Width" option, choose a small gap width to reduce the white space between bars.
   
9. In the "Legend Options" tab, choose to show the legend.
   
10. To adjust the time scale on the X-axis, right-click on the axis and choose "Format Axis". Under "Axis Options", set the minimum and maximum values for the axis and adjust the major and minor tick marks as needed.
    
11. To adjust the Y-axis scale, right-click on the axis and choose "Format Axis". Under "Axis Options", set the minimum and maximum values for the axis and adjust the major and minor tick marks as needed.
    
12. Finally, adjust the chart title and labels as needed to make it more informative and easy to understand.

Your waterfall chart is now ready! It should show the gradual reduction from 80% to 5% due to implementation of the various initiatives.