What does the time column mean on the arch pages?

Currently the column 'time' displays the timespan the package listed under the column 'Building' is actually building.
Keep in mind that the HTML pages are updated as described under How often are these pages updated? and therefore the listed timespans are not very accurate. The faster the buildd is, the more inaccurate the times might be (compared to the build time from the build logs). But this is a feature in progress....