How to replace published date?

Since theme already output both published time and modified time but display-none the latter, in this case we can just use CSS to swap the display-none.

so use this in Child Theme’s stylesheet, or via Appearance > Customize > Additional CSS

/* for post modified */
.entry-date.published { display: none; }
.updated:not(.published) { display: inline-block; }

/* for post that never been modified, theme uses .updated */
.entry-date.published.updated { display: inline-block; }

For reference
https://themes.trac.www.ads-software.com/browser/smart-magazine/1.1.0/inc/template-tags.php#L14

Great, thank you!