Option 1
config.toml
[frontmatter]
date = [':filename', ':default']
See:
https://gohugo.io/getting-started/configuration/#configure-dates
:filename
Fetches the date from the content file’s filename. For example,2018-02-22-mypage.mdwill extract the date2018-02-22. Also, ifslugis not set,mypagewill be used as the value for.Slug.
Option 2
archetypes/default.md
title = '{{ replace .Name "-" " " | title }}'
date = {{ or (os.Getenv "HUGO_DATE") .Date }}
draft = false
Then create a new page with
HUGO_DATE=2008-01-15 hugo new foo.md