PHP - Date Time Format In Nusoap.php

Hi all,

I am working on my PHP script to set up the date with the time for the autoresponder so I can send out the emails at the specific time. I need some help with set up the correct day date with the time, because on my code when I have two different times `06:00` and `20:00`, as both of them will show the time with the current day date, e.g: 28-11-2019. I find that my code have set up the date as incorrect because the time I have `06:00` which it should have set up with the next day date, e.g 29-11-2019 instead of 28-11-2019 and the time `20:00` should set up with the current day date as my current time is `15:26pm` right now. 

Output for `$autoresponder_date`:

    2019-11-25 06:00
    2019-11-25 20:00

Output for `$get_time`:

    06:00
    20:00

Here is the code:

$auto_responders = $link->prepare('SELECT * FROM autoresponder WHERE campaign = ? ORDER BY id ASC');
    $auto_responders->execute([$campaign]);
    $auto_responders->setFetchMode(PDO::FETCH_ASSOC);
    $auto_responders = $auto_responders->fetch(PDO::FETCH_ASSOC);
    $get_time = $auto_responders['send_time'];
    
    if ($get_time >= strtotime('00:00'))
    {
        $autoresponder_date = date('Y-m-d', strtotime($get_time . ' +1 day'));
    }
    else
    {
       $autoresponder_date = date('Y-m-d', strtotime($get_time));
    }
    $send_time = $autoresponder_date . ' '. date('H:i ', strtotime($get_time));

Can you please show me an example how I can set up the day date for the time `06:00` and `20:00` as if I have the time is `06:00` then check if the time have passed before I could do anything to send the email and it is the same for the time `20:00:00`? 

Thank you.