Print page created / last updated

How do I print when a page was created and last changed, e.g. in the footer for a normal page (not for a blog)?

If I use:

{{ page.modified()|date("m/d/Y") }}
{{ page.created()|date("m/d/Y") }}
{{ page.published()|date("m/d/Y") }}

I get:

02/02/2018
02/02/2018
01/01/1970

The page.modified function seems to reflect the correct date (page was changed today), but page.created returns the same value and page.published something completely off (perhaps this related to testing this with php -S?)

Thanks for any help in advance!