def METHOD_NAME (self, freq):
    (yr, mo, day, hr, min, sec, wd, jday, dst) = time.localtime(time.time())
    if freq == 'daily':
        return time.mktime((yr,mo,day+1, 0,0,0, 0,0,-1))
    elif freq == 'weekly':
        return time.mktime((yr,mo,day-wd+7, 0,0,0, 0,0,-1)) # wd(monday)==0
    elif freq == 'monthly':
        return time.mktime((yr,mo+1,1, 0,0,0, 0,0,-1))
    else:
        return None                  # not a date-based backup