The class is used to print the label "new" (or something else) as text or graphics if the item labeled is only a certain number of days old.
new_label is able to take the time values directly out of a mysql table "date" field. (no conversion needed for that)
If a certain number of days is over, the "new" label will not show up any more for the labeled item. If you change anything on your page you can label it 'changed' or 'new info' instead of 'new'. The string for 'new' is user defineable and does not really have to be 'new'.