How do I change the default date/time format?

I prefer to use the default date of MMMM/DD/YY, (written as January 23, 2018), and the time of HH:MM:SS AM/PM.

I click on the Insert Field button, and I have to manually change the date and time format every single time, which I find very annoying. I can’t find anywhere on how I am supposed to change it to default. There should be a way to change it to default, because now when I insert the time field it’s formatted as HH:MM:SS (24hr)

I am trying to do this on LibreOffice Writer on version 5.2.7.2 with the build ID of 1:5.2.7-1+rpi1+deb9u3

The default formats (date/time, currency, fixed/scientific/percent; in long/medium/short variants where applicable) depend on cell/field/… language, and are hardcoded in the corresponding locale data (see i18npool/source/localedata/data for the locale data definitions). They are not configurable (unless you rebuild LibreOffice).

You may want to create a macro to automate insertion of fields with desired format; please see this question for details.

This is a bug, and should be fixed. Of course if I enter it as bug into bugzilla, it will be reclassified as a feature request. Then, after a while, it will be classified as “won’t fix.” Welcome to LibreOffice!

It is incredible to me that there is no answer to this simple setting problem. I’ve been searching the site for a week. If anyone knows how to set the default insert date format to one of those on the list, please tell us. Thank you.

Create your own cell style(s) for dates and times to override the default. You may want to do the same for currencies, text cells and measurement units. Store these stlyes in a template and make it your default templates.
Styles can be assigned to keyboard shortcuts.