@Harper ,
Based on your description, I think you may need to re-select data for your chart.
- Please back up Excel file, and then remove and re-create a new Line chart.
- Select the chart, and go to Chart Deign tab, click Select Data.
- Edit Legend Entries and Horizontal Axis Labels as needed.
- Click Edit. In my test, I set the time column as the horizontal axis label.
Besides, I found this Customize charts Video, you could also have a look.
Hope the information could be helpful to you. Any updates, please let me know.
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