PHP - Time() Capturing Wrong Time

What are the differences and implications of UTC time and Zulu time?
  

<?php
function getArr(string $time):array
{
    $dateTime = new \DateTime($time);
    return [
        'time'=>$time,
        'timestamp'=> $dateTime->getTimestamp(),
        'dateTime' => $dateTime
    ];
}
$arr = getArr('2020-08-05');  
$arr_z = getArr('2020-08-05T00:00:00Z');  

print_r($arr);
print_r($arr_z);

echo('equal timestamps: '.($arr['timestamp'] === $arr['timestamp']?'true':'false'));

Array
(
    [time] => 2020-08-05
    [timestamp] => 1596585600
    [dateTime] => DateTime Object
        (
            [date] => 2020-08-05 00:00:00.000000
            [timezone_type] => 3
            [timezone] => UTC
        )

)
Array
(
    [time] => 2020-08-05T00:00:00Z
    [timestamp] => 1596585600
    [dateTime] => DateTime Object
        (
            [date] => 2020-08-05 00:00:00.000000
            [timezone_type] => 2
            [timezone] => Z
        )

)
equal timestamps: true

Let's say I am buying a share for $10.

If I sell the share on the same day BEFORE 3:30PM, it will be sold for $10, but if I keep the share past 3:30PM, I want the code to automatically add $1 (Taxes and such) once in the the price of the share in database, after that no matter how many days pass by, the price will remain the same.

I've thought about CRON jobs, but I have no idea how to make/use them or set them up.

Any direction or help is appreciated.

Question:
For a website on a shared server (regardless of server location), is there such a thing as PHP code that will consistently produce my own time zone's time without having to adjust every few months?

Background:
No matter how much I "adjust" the code, time zones, etc., things like daylight saving time, or server location throws it off by 1, 2, sometimes 3 hours.

Example:
This is my code:
$date = new DateTime();
$currentTime = $date->sub(new DateInterval('PT8H'))->format('F j, Y \a\t g:ia');

The Pacific ("Los Angeles") time right now is 7:58pm, but my code says it's 6:58pm. So now I have to go in and correct the "PT8H" portion. I'm wondering if there is some code I can use whereby I can simply "set it and forget it."

Thank you!