şöyle deneyiniz

function your_prefix_post_date( $output ) {
$output = "";
$format = apply_filters( 'astra_post_date_format', ” );
$modified_date = esc_html( get_the_modified_date( $format ) );
$updatetxt = “Last Updated on"";
$postedtxt = “Posted on"";
$u_time = get_the_time('U');
$u_modified_time = get_the_modified_time('U');
$modified_on = sprintf(
esc_html( '%s', '%s'),
$modified_date
);

if ($u_modified_time >= $u_time + 86400) {
$output .= "";
$output .= ' ' . $updatetxt . "";
$output .= ' ' . $modified_on . "";
$output .= "";
return $output;
}

else {

$output .= "";
$output .= ' ' . $postedtxt . "";
$output .= ' ' . $modified_on . "";
$output .= "";
return $output;
}
}
add_filter( 'astra_post_date', 'your_prefix_post_date' );
add_filter( 'astra_post_meta_separator', '__return_false' );