PHP check if two date have 48hours difference [duplicate]

$datetime 1 is the date generate every day, $datetime2 is the date of my article post.

I want that say if some article post have 48 hours difference between today and date of post.

$datetime1 = date('d/m/Y');
$datetime2 =get_field('data_intervento');
$a = strtotime($datetime1);
$b= strtotime($datetime2);
echo ($a - $b)/3600;

but something not work

source https://stackoverflow.com/questions/75998281/php-check-if-two-date-have-48hours-difference