--time-style=TIME_STYLE
      time/date format with -l; see TIME_STYLE below

full-iso, long-iso, iso, locale, +FORMAT

man에 나와있는 설명. -l 옵션과 같이 써야함.

아래는 사용 예시

[root@host-10-101-0-10 yeonghoon.kim]# ls -l --time-style=full-iso
합계 12
drwxr-xr-x  2 ioniere ioniere 4096 2019-11-18 03:43:01.525012082 +0900 db_backup
drwxr-xr-x 18 ioniere ioniere 4096 2019-11-18 10:41:58.360339510 +0900 public_html
drwxr-xr-x  2 ioniere ioniere 4096 2019-11-18 03:43:01.644013163 +0900 source_back

[root@host-10-101-0-10 yeonghoon.kim]# ls -l --time-style=long-iso
합계 12
drwxr-xr-x  2 ioniere ioniere 4096 2019-11-18 03:43 db_backup
drwxr-xr-x 18 ioniere ioniere 4096 2019-11-18 10:41 public_html
drwxr-xr-x  2 ioniere ioniere 4096 2019-11-18 03:43 source_backup

[root@host-10-101-0-10 yeonghoon.kim]# ls -l --time-style=iso
합계 12
drwxr-xr-x  2 ioniere ioniere 4096 11-18 03:43 db_backup
drwxr-xr-x 18 ioniere ioniere 4096 11-18 10:41 public_html
drwxr-xr-x  2 ioniere ioniere 4096 11-18 03:43 source_backup

[root@host-10-101-0-10 yeonghoon.kim]# ls -l --time-style='+%Y%m%d'
합계 12
drwxr-xr-x  2 ioniere ioniere 4096 20191118 db_backup
drwxr-xr-x 18 ioniere ioniere 4096 20191118 public_html
drwxr-xr-x  2 ioniere ioniere 4096 20191118 source_backup