We consider how dates are recorded and how they might be rendered in aggregate.
We now date every action to the millisecond as it happens. This hasn't always been the case. There are plenty of old pages with no dates what so ever.
We've created a markup for dates and date ranges that would be well suited for historical timelines where the '60s might be a period of interest. See About Calendar Plugin
We've created a markup for periodic reporting from wiki pages. This markup renders as a count-down clock on the page warning you that you'd better get writing if you want to be in the next report issue. See About Report Plugin
The journal collects all actions for a page. This includes time of edit for all editors through the history of the page.
The sitemap for a site lists the last edit time for each page on the site, not counting forks as edits.
The neighborhood collects sitemaps and associated dates for sites found by browsing.
The lineup collects the pages currently opened and potentially in view of the user interface.
The community roster collects site names and possibly page dates from their sitemaps. See About Roster Plugin
Action dates are shown in hovers and as a bold timestamp on recalled revisions.
Sitemap last edit dates are shown in Recent Changes for the current neighborhood. See About Activity Plugin
Lineup activity is shown by day over eight weeks in from the 'hamburger' menu in the footer.
Conversation Clubs create a variation of Recent Changes based on a roster rather than neighborhood.
A longer range and more detailed activity map has been suggested based on that of the original wiki. post