- Click Format > Edit Script Formats.
- On the right, click the Scene Headings button.
- In the middle of the screen, go to Time-of-Day Dashes and change the number to one.
- Click OK.
Note: this will only change new scene headings not existing ones.
To change existing Scene Headings use Search > Search & Replace (Search > Find/Replace on Mac). Search for the Time-of-Day, including the dashes (e.g., "-- NIGHT"). Replace with one dash (e.g., "- NIGHT").