Currently, the launch date of a site is only shown as a relative timestamp. That's fine if this happened recently, but for example Bitcoin's page says the site was launched "1 year ago". That's rather vague; one has to find the graduation post on a site's own Meta to see the actual launch date (1 year and 10(!) months ago).
Most relative timestamps on Stack Exchange can be hovered over to show a UTC date/time, e.g. the other ones in that column (see below). That would be an option; alternatively, the launch date could be added as a separate 'event' just above 'public beta start'.