PHP TIME _filter()

<?php

TIME_THIS_WEEK;
  echo  strtotime("last Monday");                   #2017/1/2 0:0:0
TIME_THIS_MONTH;
  echo  strtotime(date("Y-m-1"));                   #2017/1/1 0:0:0
TIME_LAST_MONTH;
  $last_month_time = strtotime("last Month");
  echo  strtotime(date("Y-m-1", $last_month_time)); #2016/12/1 0:0:0
  echo  strtotime(date("Y-m-1"));          #REPEAT  #2017/1/1 0:0:0