If you would like to hide the duration column in your Rundown, you can do that via the Manage Columns window.
Click the three dots in the top right corner of your Rundown
Then selecting Manage Columns
From here you can select the little eye icon on the right to hide the duration column
When you have hidden a column it will have a cross through the eye
To unhide, simply click the eye again.
Please note these changes will be reflected for your whole team - so you are hiding this column for everyone in your Project not just you.
Hit "Save & Close" in the bottom right corner of your window when you have made your changes.