Summary:

Date/time field column widths are automatically resized in list screens

More information:

This is by design, but a workaround has been created if users would like all of the column headers to be resized equally. This workaround is as follows:

There is a width on the date columns that can be seen when viewing the source of the page. If this width is removed, the columns will automatically resize. 

  1. Create the fields you want to use and add them to the list you want (opportunity list).
  2. When viewing the opportunity page, make sure both columns are shown and press F12
  3. Now the source code should be shown and you can check what entry type the field in question is. In this case, my field entrytype was 42
    Description
  4. The next step is to go back to the opportunity list (in customisation -> opportunity -> lists)
  5. Add the following script to the custom content, ensuring that the entrytype is the same as the one on the page as shown above

<script>

$(document).ready(function () {

      $('td[entrytype="42"]').removeAttr("width");

});

</script>

    6.   Save the list and go back to the opportunity page
    7.   Ensure that the changes are working correctly