With this function you can get the number of seconds between two
dates. The return value is always positive and will be a whole
diff = date_second_span(date_create_datetime(2011, 9, 15, 11, 4, 0 ), date_current_datetime());
This would set "diff" to the number of seconds between 15th September 2011, 11:04 and the current date and time.