The Modified Date Block will display the date on which the current Page or Post was last modified. This is different from the Post Date Block which shows the date at which the Page or Post was first published. Although you can add this block into your normal Page or Post content, it will be more useful adding it to your theme’s templates using the Full Site Editor.
Once you've added the block, there are further options available in the Settings Sidebar. You can change the Text, Background and Link colours, and you can also change various Typography settings like Font size, Appearance, Decoration, Line height, Letter case & Letter spacing.
The date can be displayed in the default format, or if you turn off the Default Format switch in the Settings Sidebar, you can select from a number of other formats or provide a custom date format. If the Display Last Modified Date switch is turned on, then the last modified date is only shown if the post has been modified, otherwise it displays the published date.
The various options for this block are located within separate Settings () and Styles () tabs, in the Settings Sidebar.