Date specifications used by macOS are based on sophisticated technologies which ensure that the specifications can be used and transferred universally, i.e. independent of language, notational conventions, calendar systems, and time zones. For this reason, macOS always stores a time and time zone specification together with each date, even if the application using this date might interpret it “without wall clock time” as a specification for a particular day in a calendar only.
PrefEdit lets you choose how date entries should be presented:
You can change this preference setting as follows:
In older versions of macOS Settings are called Preferences.
The setting becomes effective both for the display and the entry of dates within PrefEdit. When you have chosen the setting to include the time specifications for dates, dates must be entered with wall clock time afterwards. The entered time represents the local time in your current time zone. This setting does not influence how macOS stores date entries internally. Omitting the time during date entry does not save any memory or storage space. If omitting time specifications, date entries will be interpreted as time specifications of midnight in the local time zone, e.g. March 26, 2017 is actually represented as March 26, 2017, 00:00:00 local time, and will be saved after being converted to the Universal Time Coordinated (UTC) time zone. It is up to the application processing the date entry later whether it should take the plain date into account only or should also consider the time.
In additional to the general preference setting, you can also temporarily change the date/time mode on a window-by-window basis. This is helpful if you only need to specify the time in one particular document, but not in others.