mail.ui.display.dateformat.today 	
mail.ui.display.dateformat.thisweek 	
mail.ui.display.dateformat.default

 Value 	Meaning 	Example date and time
0 	No date 	10:23 AM
1 	Your system's long* date format 	Friday, December 31 2003 10:23 AM
2 	Your system's short* date format 	12/31/1999 10:23 AM
3** 	Year and month, separated by a slash 	1999/12 10:23 AM
4** 	Abbreviated day name 	Fri 10:23 AM 
* Some operating systems have only one date format. On these systems, the values 1 and 2 
  produce the same result.
** Values 3 and 4 were not supported in Thunderbird version 53 (due to switching to 
  ICU/CLDR) but got implemented again in version 54. They stopped working again in 
  Thunderbird 83. Value 4 (day name) was restored in version 91. 

what are you changing in the config editor? why? Seriously I have the time displayed, but generally I have he column width set to not show more that the date and the ellipse that indicates there is more to show. But I mostly do not care about space. By having my email view in the bottom half of the screen (wide view), I have amply horizontal space across my monitor for folder and email lists. Sadly most folk want to emulate that three columns look that Outlook has and then undertake a long standing battle to get everything in a restricted space and have wrapped headings and multi line displays that turns the list into something that is no longer really a list. I the interests of brevity, I will assume you are messing with; mail.ui.display.dateformat.today mail.ui.display.dateformat.thisweek mail.ui.display.dateformat.default These preferences manage the display of messages for today, this week and everything else respectively. Teey can be set to Value Meaning Example date and time 0 No date 10:23 AM 1 Your system's long* date format Friday, December 31 2003 10:23 AM 2 Your system's short* date format 12/31/1999 10:23 AM 3** Year and month, separated by a slash 1999/12 10:23 AM 4** Abbreviated day name Fri 10:23 AM * Some operating systems have only one date format. On these systems, the values 1 and 2 produce the same result. ** Values 3 and 4 were not supported in Thunderbird version 53 (due to switching to ICU/CLDR) but got implemented again in version 54. They stopped working again in Thunderbird 83. Value 4 (day name) was restored in version 91. None of that really covers what you are talking about, but it is the only related preference I can think of that has 0-4 as options. I think what you are seeking is to change the display format of dates in the mail list. The intl.date_time.pattern_override preferences would appear to be the wayt to do this. See https://support.mozilla.org/en-US/kb/customize-date-time-formats-thunderbird#w_create-date-and-time-format-override-preferences-using-thunderbirds-config-editor See as my references https://kb.mozillazine.org/Date_display_format and https://support.mozilla.org/en-US/kb/customize-date-time-formats-thunderbird