Microsoft is testing a new feature in the Windows 10 19H1*Insider builds (Build 1903) that changes how dates are displayed in File Explorer to a more "conversational format" such as "minutes ago", "yesterday", "hours ago", etc.
In the release notes for Windows Insider build 18272, Microsoft stated that some insiders may notice changes in File Explorer.
"Some Insiders may notice small differences in File Explorer over the coming flights – we’ll have more to share later about this later."
One of the changes that is being tested is to display the "Date Modified" times in a new format that is being called internally as "FriendlyDates" or in the settings as "Conversational Format". This new format uses time references such as "hour ago", "today", or "yesterday", which is similar to how we would discuss timeframes when having*a conversation with someone.*
Historically, File Explorer would list the dates in different formats depending on your region. They would always include the month, date, year, and time. For example, "day/month/year hour:minute" or "month/day/year hour:minute".
Historical Date Formats Showing Month, Date, Year, and Time
With the new "Conversational Format" the Date Modified column is either shown as a string, a string with a time, a shortened date, or the full date. Below you can see an example directory where we created folders at different times to illustrate the strings used.
New Conversational Format
The conversational format strings that we saw listed include:

  • Just Now - File modifications done just now.
  • minute(s) ago*(16 minutes ago) - File modifications done on the same day but less than an hour ago.
  • hour(s) ago (2 hours ago)*- File modifications done on the same day but over an hour ago.
  • Yesterday with time (Yesterday at*07:13)*- File modifications done the previous day.
  • Day of week at time (Tue at 06:44) - File modifications done two days ago.
  • Month Day (October 7)*- File modification times older than two days and in the same year.
  • Month Day, Year (December 7, 2017)*- File modification times over a year old.

It also appears that the format is stuck in "Month Day", ie December 7, regardless of what geographic region you are in.
If you are part of the test, you can enable/disable the conversational format by going into the View tab of File Explorer, clicking the*Options*button, and then selecting the View tab in Folder options as shown below. When you scroll down you will see a "Show dates in conversational format" checkbox that you can check or uncheck to disable the feature.
Caption
Personally, I hate this new format and prefer to see a date and time so that I can easily compare file dates. As long as they keep this as a configurable option, though, I see no harm in it.