Assumindo o GNU ls, de info ls "Formatting file timestamps"
:
'--time-style=STYLE' List timestamps in style STYLE. The STYLE should be one of the following:
...
'long-iso' List ISO 8601 date and time in minutes, e.g., '2002-03-30 23:45'. These timestamps are shorter than 'full-iso' timestamps, and are usually good enough for everyday work. This style is equivalent to '+%Y-%m-%d %H:%M'.
...
You can specify the default value of the '--time-style' option with the environment variable 'TIME_STYLE'; if 'TIME_STYLE' is not set the default style is 'locale'.
Portanto, coloque o seguinte em .bashrc
ou .bash_profile
e está tudo pronto:
export TIME_STYLE=long-iso