Update mySQL rows after specified time (PHP, MySQL)

I would attack this problem like this:

add expiration date column un user table
add there timestamp to what datetime account should be valid.

When user is logging in, PHP is checking the 'epxiration' 
column and check if datetime value is still valid.

You can do like rescan data function that will check the 'expiration' column values.

  For example if the date expired more that 6 month ago, 
row will be deleted.

You can add this like autofeature whenever app starts or admin is loggin in.

   For example make table 'Cleaning time' and
 there 'Last Cleaning Date' 'Next Cleaning Date' 
'Cleaning step';

Make the app to check the table each times script runs if the Cleaning date is === today, just make it to rescan users and delete other ones.

Then just change the 'Cleaning time date' by adding 'Step value' to the 'Last cleaning date'

btw. always use serwer time to manage data

You can calculate the period the user was enabled by using date and strtotime functions in php. After that you can trigger a query if the current date matches with your calculated date.

//---for calculating future date  
$newtimestamp = strtotime( "october, 26, 2015" );
$expmonth = date( 'm', $newtimestamp );

//---for calculating current date  
$currenttimestamp = date();
$currentmonth = date( 'm', $currenttimestamp );

//--if both date match then execute query
if ($expmonth == $currentmonth) {
  //write your update query here.
}

The correct way is to run cronjob daily on server which checks user expiration date and change it's status. If you want to test on local server you do not need any scheduler just hit the url which checks the user expiration and changes its status. if you have linux hosting you need only to set cron job by executing a command like wget -O /dev/null http://www.example.com/cronit.php

I think cron job will be good for you . You will just need to make a script and run that in a your specific time . That's It.