PHP Better Precise Time Unit than microtime()

Time.php

<?php
declare(strict_types=1);

use function hrtime;
use function intdiv;
use function microtime;

/**
 * Time helper class to get the current time in milliseconds, microseconds, and nanoseconds
 * Use boot time to get the time since the application booted and more precise time than microtime
 */
final class Time
{
    /**
     * @var int $bootTimeNano The boot time in nanoseconds
     */
    private static int $bootTimeNano;

    /**
     * Get the boot time in nanoseconds
     *
     * @return int
     */
    public static function boot(): int
    {
        return self::$bootTimeNano ??= (int)(microtime(true) * 1_000_000_000) - hrtime(true);
    }

    /**
     * Get the current second time
     *
     * @return int
     */
    public static function second() : int
    {
        return intdiv(self::nano(), 1_000_000_000);
    }

    /**
     * Get the current millisecond time
     *
     * @return int
     */
    public static function milli() : int
    {
        return intdiv(self::nano(), 1_000_000);
    }

    /**
     * Get the current micro time
     *
     * @return int
     */
    public static function micro() : int
    {
        return intdiv(self::nano(), 1_000);
    }

    /**
     * Get the current nano time
     *
     * @return int
     */
    public static function nano() : int
    {
        return self::boot() + hrtime(true);
    }
}