SQL Server sortable UUID in C#

GenerateSqlServerSortableTimeBasedGuid.cs

using System;
using System.Threading;

namespace GenerateSqlServerSortableTimeBasedGuid_App
{

    internal class Program
    {
        static readonly Random random = new Random();

        /**
         * The sorting of SQL Server is rather confusing and incompatible with UUIDv6 and UUIDv7.
         * Therefore this method generates UUID which are sortable by SQL Server.
         * Version 1: Resolution of 1 milliseconds, random part of 16 bits, local timezone, 48 zero bits "signature", NOT UUIDv8 conform.
         * Version 2: Resolution of 1 milliseconds, random part of 16 bits, UTC time, 48 bit random "signature", UUIDv8 conform.
         * C# implementation: https://gist.github.com/danielmarschall/7fafd270a3bc107d38e8449ce7420c25
         * PHP implementation: https://github.com/danielmarschall/uuid_mac_utils/blob/master/includes/uuid_utils.inc.php
         */
        public static Guid GenerateSqlServerSortableTimeBasedGuid(int hickelUuidVersion = 2)
        {
            string block1, block2, block3, block4, block5;
            DateTime dt;

            // The sorting in SQL Server is like this:

            // First Sort block 5, nibbles from left to right (i.e. 000000000001 < 000000000010 < ... < 010000000000 < 100000000000)
            if (hickelUuidVersion == 1)
            {
                block5 = "000000000000";
            }
            else if (hickelUuidVersion == 2)
            {
                block5 = "5ce32bd83b96";
            }
            else
            {
                throw new Exception("Invalid version");
            }

            // Then: Sort block 4, nibbles from left to right
            if (hickelUuidVersion == 1)
            {
                dt = DateTime.Now;
                block4 = String.Format("{0:yy}{1:D2}", dt, (int)Math.Floor((decimal)dt.Year/100)); // Example: 0x2420 = 2024
            }
            else
            {
                dt = DateTime.UtcNow;
                int variant = 0x8; // First nibble needs to be 0b10_ (0x8-0xB) for RFC 9562. We use it to store 2 more random bits.
                int unused2bits = 0; // Cannot be used for random, because it would affect the sorting
                block4 = String.Format("{0:X1}{1:X3}", variant + (unused2bits & 0x3), dt.Year);
            }

            // Then: Sort block 3, bytes from right to left (i.e. 0100 < 1000 < 0001 < 0010)
            if (hickelUuidVersion == 1)
            {
                block3 = String.Format("{0:ddMM}", dt);
            }
            else
            {
                int uuidVersion = 8; // First nibble needs to be "8" for "UUIDv8 = Custom UUID"
                block3 = String.Format("{0:X1}{1:X3}", uuidVersion, dt.DayOfYear/*1..366*/); 
            }

            // Then: Sort block 2, bytes from right to left
            if (hickelUuidVersion == 1)
            {
                block2 = String.Format("{0:mmHH}", dt);
            }
            else
            {
                int minuteOfDay = (dt.Minute + dt.Hour * 60) + 1; // 1..1440
                block2 = String.Format("{0:X4}", minuteOfDay);
            }

            // Then: Sort block 1, bytes from right to left
            int millisecond8bits = (int)Math.Round(((decimal)dt.Millisecond / 999) * 255); // deviation -2ms..2ms
            if (hickelUuidVersion == 1)
            {
                int rnd16bits = random.Next(0x0000, 0xFFFF);
                block1 = String.Format("{0:X4}{1:X2}{2:ss}", rnd16bits, millisecond8bits, dt);
            }
            else
            {
                int rnd16bits = random.Next(0x0000, 0xFFFF + 1);
                block1 = String.Format("{0:X4}{1:X2}{2:X2}", rnd16bits, millisecond8bits, dt.Second);
            }

            // Now build and parse UUID
            string sGuid = String.Format("{0}-{1}-{2}-{3}-{4}", block1, block2, block3, block4, block5);
            Thread.Sleep((int)Math.Ceiling((decimal)999 / 255)); // Make sure that "millisecond" is not repeated on this system
            return Guid.Parse(sGuid);
        }

        static void Main(string[] args)
        {
            Console.WriteLine(DateTime.Now);
            Guid test;
            test = GenerateSqlServerSortableTimeBasedGuid(1);
            Console.WriteLine(test);
            test = GenerateSqlServerSortableTimeBasedGuid(2);
            Console.WriteLine(test);
        }
    }

}