Take C{quantity}, C{modifier} and C{unit} strings and convert them into values.
        After converting, calcuate the time and return the adjusted sourceTime.

        @type  source:   time
        @param source:   time to use as the base (or source)
        @type  quantity: string
        @param quantity: quantity string
        @type  modifier: string
        @param modifier: how quantity and units modify the source time
        @type  units:    string
        @param units:    unit of the quantity (i.e. hours, days, months, etc)

        @rtype:  struct_time
        @return: C{struct_time} of the calculated time

def _buildTime(self, source, quantity, modifier, units):
        """
        Take C{quantity}, C{modifier} and C{unit} strings and convert them into values.
        After converting, calcuate the time and return the adjusted sourceTime.

        @type  source:   time
        @param source:   time to use as the base (or source)
        @type  quantity: string
        @param quantity: quantity string
        @type  modifier: string
        @param modifier: how quantity and units modify the source time
        @type  units:    string
        @param units:    unit of the quantity (i.e. hours, days, months, etc)

        @rtype:  struct_time
        @return: C{struct_time} of the calculated time
        """
        if _debug:
            print '_buildTime: [%s][%s][%s]' % (quantity, modifier, units)

        if source is None:
            source = time.localtime()

        if quantity is None:
            quantity = ''
        else:
            quantity = quantity.strip()

        if len(quantity) == 0:
            qty = 1
        else:
            try:
                qty = int(quantity)
            except ValueError:
                qty = 0

        if modifier in self.ptc.Modifiers:
            qty = qty * self.ptc.Modifiers[modifier]

            if units is None or units == '':
                units = 'dy'

        # plurals are handled by regex's (could be a bug tho)

        (yr, mth, dy, hr, mn, sec, _, _, _) = source

        start  = datetime.datetime(yr, mth, dy, hr, mn, sec)
        target = start

        if units.startswith('y'):
            target        = self.inc(start, year=qty)
            self.dateFlag = 1
        elif units.endswith('th') or units.endswith('ths'):
            target        = self.inc(start, month=qty)
            self.dateFlag = 1
        else:
            if units.startswith('d'):
                target        = start + datetime.timedelta(days=qty)
                self.dateFlag = 1
            elif units.startswith('h'):
                target        = start + datetime.timedelta(hours=qty)
                self.timeFlag = 2
            elif units.startswith('m'):
                target        = start + datetime.timedelta(minutes=qty)
                self.timeFlag = 2
            elif units.startswith('s'):
                target        = start + datetime.timedelta(seconds=qty)
                self.timeFlag = 2
            elif units.startswith('w'):
                target        = start + datetime.timedelta(weeks=qty)
                self.dateFlag = 1

        return target.timetuple()