(original explanation made from 7.0 branch, now targeting 6.4 cf comments)

The related issue, when i explained the possible solution : #52880

On Symfony\Bridge\Doctrine\DataCollector\DoctrineDataCollector, updated the native return type from int to float for the method getTime.

Context :

    public function getTime(): int
    {
        $time = 0;
        foreach ($this->data['queries'] as $queries) {
            foreach ($queries as $query) {
                $time += $query['executionMS'];
            }
        }

        return $time;
    }

Inside this method, the value of $time was always a float smaller than 0. The transition to native return type (which was correct regarding to old phpdoc type) made the return cast int to the floating value, hence returning always 0.

I updated the return type to float and updated the test to check for the calculus on floating values.
I had to switch to usleep instead of sleep, since the value might not be an int.