PHP find difference between two datetimes

I'm not sure what format you're looking for in your difference but here's how to do it using DateTime

$datetime1 = new DateTime();
$datetime2 = new DateTime('2011-01-03 17:13:00');
$interval = $datetime1->diff($datetime2);
$elapsed = $interval->format('%y years %m months %a days %h hours %i minutes %s seconds');
echo $elapsed;

You can simply use datetime diff and format for calculating difference.

<?php
$datetime1 = new DateTime('2009-10-11 12:12:00');
$datetime2 = new DateTime('2009-10-13 10:12:00');
$interval = $datetime1->diff($datetime2);
echo $interval->format('%Y-%m-%d %H:%i:%s');
?>

For more information OF DATETIME format, refer: here
You can change the interval format in the way,you want.

Here is the working example

P.S. These features( diff() and format()) work with >=PHP 5.3.0 only

John Conde does all the right procedures in his method but doesn't satisfy the final step in your question which is to format the result to your specifications.

This code (Demo) will display the raw difference, expose the trouble with trying to immediately format the raw difference, display my preparation steps, and finally present the correctly formatted result:

$datetime1 = new DateTime('2017-04-26 18:13:06');
$datetime2 = new DateTime('2011-01-17 17:13:00');  // change the millenium to see output difference
$diff = $datetime1->diff($datetime2);

// this will get you very close, but it will not pad the digits to conform with your expected format
echo "Raw Difference: ",$diff->format('%y years %m months %d days %h hours %i minutes %s seconds'),"\n";

// Notice the impact when you change $datetime2's millenium from '1' to '2'
echo "Invalid format: ",$diff->format('%Y-%m-%d %H:%i:%s'),"\n";  // only H does it right

$details=array_intersect_key((array)$diff,array_flip(['y','m','d','h','i','s']));

echo '$detail array: ';
var_export($details);
echo "\n";

array_map(function($v,$k)
    use(&$r)
    {
        $r.=($k=='y'?str_pad($v,4,"0",STR_PAD_LEFT):str_pad($v,2,"0",STR_PAD_LEFT));
        if($k=='y' || $k=='m'){$r.="-";}
        elseif($k=='d'){$r.=" ";}
        elseif($k=='h' || $k=='i'){$r.=":";}
    },$details,array_keys($details)
);
echo "Valid format: ",$r; // now all components of datetime are properly padded

Output:

Raw Difference: 6 years 3 months 9 days 1 hours 0 minutes 6 seconds
Invalid format: 06-3-9 01:0:6
$detail array: array (
  'y' => 6,
  'm' => 3,
  'd' => 9,
  'h' => 1,
  'i' => 0,
  's' => 6,
)
Valid format: 0006-03-09 01:00:06

Now to explain my datetime value preparation:

$details takes the diff object and casts it as an array. array_flip(['y','m','d','h','i','s']) creates an array of keys which will be used to remove all irrelevant keys from (array)$diff using array_intersect_key().

Then using array_map() my method iterates each value and key in $details, pads its left side to the appropriate length with 0's, and concatenates the $r (result) string with the necessary separators to conform with requested datetime format.