How to differenciate between date post and current time

The following Code will differenciate between date post and current time

<?php
date_default_timezone_set('Africa/Lagos');
function convert($datetime){
  $time=strtotime($datetime);
  $diff=time()-$time;
  $diff/=60;
  $var1=floor($diff);
  $var=$var1<=1 ? 'min' : 'mins';
  if($diff>=60){
    $diff/=60;
    $var1=floor($diff);
    $var=$var1<=1 ? 'hr' : 'hrs';
    if($diff>=24){$diff/=24;$var1=floor($diff);$var=$var1<=1 ? 'day' : 'days';
    if($diff>=30.4375){$diff/=30.4375;$var1=floor($diff);$var=$var1<=1 ? 'month' : 'months';
    if($diff>=12){$diff/=12;$var1=floor($diff);$var=$var1<=1 ? 'year' : 'years';}}}}
    echo $var1,' ',$var,' ago';
  }
  $date = date('Y-m-d H:i:s');
  echo $date; 
  echo "<br>";


$datetime="2020-04-27 12:00:00";
 echo convert($datetime);
 ?>