Vendor/phpspreadsheet/phpoffice/phpspreadsheet/src/PhpSpreadsheet/Calculation/DateTime.php
public static function HOUROFDAY($timeValue = 0)
    {
        $timeValue = Functions::flattenSingleValue($timeValue);

        if (!is_numeric($timeValue)) {
            if (Functions::getCompatibilityMode() == Functions::COMPATIBILITY_GNUMERIC) {
                $testVal = strtok($timeValue, '/-: ');
                if (strlen($testVal) < strlen($timeValue)) {
                    return Functions::VALUE();
                }
            }
            $timeValue = self::getTimeValue($timeValue);
            if (is_string($timeValue)) {
                return Functions::VALUE();
            }
        }
        // Execute function
        if ($timeValue >= 1) {
            $timeValue = fmod($timeValue, 1);
        } elseif ($timeValue < 0.0) {
            return Functions::NAN();
        }
        $timeValue = Date::excelToTimestamp($timeValue);

        return (int) gmdate('G', $timeValue);
    }
public static function HOUROFDAY($timeValue = 0)
    {
        $timeValue = Functions::flattenSingleValue($timeValue);

        if (!is_numeric($timeValue)) {
            if (Functions::getCompatibilityMode() == Functions::COMPATIBILITY_GNUMERIC) {
                $testVal = strtok($timeValue, '/-: ');
                if (strlen($testVal) < strlen($timeValue)) {
                    return Functions::VALUE();
                }
            }
            $timeValue = self::getTimeValue($timeValue);
            if (is_string($timeValue)) {
                return Functions::VALUE();
            }
        }
        // Execute function
        if ($timeValue >= 1) {
            $timeValue = fmod($timeValue, 1);
        } elseif ($timeValue < 0.0) {
            return Functions::NAN();
        }
        $timeValue = Date::excelToTimestamp($timeValue);

        return (int) gmdate('G', $timeValue);
    }
HOUROFDAY.

Returns the hour of a time value.
The hour is given as an integer, ranging from 0 (12:00 A.M.) to 23 (11:00 P.M.).

Excel Function:
HOUR(timeValue)

@param mixed $timeValue Excel date serial value (float), PHP date timestamp (integer),
PHP DateTime object, or a standard time string

@return int Hour