static void Main()
{
    while (true)
    {
        using(var fileStream = new FileStream("TestFile.txt", FileMode.OpenOrCreate, FileAccess.ReadWrite, FileShare.None))
        {
            //CallSetFileTime(fileStream);

            fileStream.Write(new byte[] { 0x77 }, 0, 1);
        }
    }
}

static void CallSetFileTime(FileStream fileStream)
{
    var hFile = fileStream.SafeFileHandle.DangerousGetHandle();

    var pLastWriteTime = Marshal.AllocHGlobal(Marshal.SizeOf(typeof(System.Runtime.InteropServices.ComTypes.FILETIME)));

    if (!GetFileTime(hFile, IntPtr.Zero, IntPtr.Zero, pLastWriteTime))
        throw new Exception();

    if (!SetFileTime(hFile, IntPtr.Zero, IntPtr.Zero, pLastWriteTime))
        throw new Exception();

    Marshal.FreeHGlobal(pLastWriteTime);
}

[DllImport("kernel32.dll", SetLastError = true, CharSet = CharSet.Auto)]
static extern bool GetFileTime(IntPtr hFile, IntPtr pCreationTime, IntPtr pLastAccessTime, IntPtr pLastWriteTime);

[DllImport("kernel32.dll", SetLastError = true, CharSet = CharSet.Auto)]
static extern bool SetFileTime(IntPtr hFile, IntPtr pCreationTime, IntPtr pLastAccessTime, IntPtr pLastWriteTime);

PD>int main(int argc, _TCHAR* argv[])
PD>{
PD>        while (true)
PD>        {
PD>            HANDLE hFile = CreateFile("TestFile.txt", GENERIC_READ | GENERIC_WRITE, 0, NULL, OPEN_ALWAYS, 0, 0);
PD>            FILETIME ft;
PD>            GetFileTime(hFile, 0, 0, &ft);
PD>            printf("%u\n", ft.dwLowDateTime);
PD>            FILETIME ft1 = { 0 };
PD>            ft.dwLowDateTime++; // с этой строчкой работает, без нее - нет
PD>            SetFileTime(hFile, 0, 0, &ft);
PD>            char cBuf = 0x77;
PD>            DWORD dwWritten;
PD>            WriteFile(hFile, &cBuf, 1, &dwWritten, NULL);
PD>            CloseHandle(hFile);
PD>        }
PD>        return 0;
PD>}
PD>

static void Main()
{
    var random = new Random();

    while (true)
    {
        using(var fileStream = new FileStream("TestFile.txt", FileMode.OpenOrCreate, FileAccess.ReadWrite, FileShare.Read))
        {
            var hFile = fileStream.SafeFileHandle.DangerousGetHandle();

            for (int i = 0; i < 10; i++)
            {
                fileStream.Write(new byte[] { (byte)random.Next(0, 255) }, 0, 1);
            }

            fileStream.Flush(true);

            SetSameFileTime(hFile);

            for (int i = 0; i < 10; i++)
            {
                fileStream.Write(new byte[] { (byte)random.Next(0, 255) }, 0, 1);
            }

            fileStream.Flush(true);

            IncFileTimeALittle(hFile);

            for (int i = 0; i < 10; i++)
            {
                fileStream.Write(new byte[] { (byte)random.Next(0, 255) }, 0, 1);
            }

            fileStream.Flush(true);
        }
    }
}

static void SetSameFileTime(IntPtr hFile)
{
    var pLastWriteTime = Marshal.AllocHGlobal(Marshal.SizeOf(typeof(System.Runtime.InteropServices.ComTypes.FILETIME)));

    try
    {
        if (!WinApi.GetFileTime(hFile, IntPtr.Zero, IntPtr.Zero, pLastWriteTime))
            throw new Exception();

        if (!WinApi.SetFileTime(hFile, IntPtr.Zero, IntPtr.Zero, pLastWriteTime))
            throw new Exception();
    }
    finally
    {
        Marshal.FreeHGlobal(pLastWriteTime);
    }
}

static void IncFileTimeALittle(IntPtr hFile)
{
    var pLastWriteTime = Marshal.AllocHGlobal(Marshal.SizeOf(typeof(System.Runtime.InteropServices.ComTypes.FILETIME)));

    try
    {
        if (!WinApi.GetFileTime(hFile, IntPtr.Zero, IntPtr.Zero, pLastWriteTime))
            throw new Exception();

        var fileTime = (System.Runtime.InteropServices.ComTypes.FILETIME)Marshal.PtrToStructure(pLastWriteTime, typeof(System.Runtime.InteropServices.ComTypes.FILETIME));

        fileTime.dwHighDateTime++;

        Marshal.StructureToPtr(fileTime, pLastWriteTime, false);

        if (!WinApi.SetFileTime(hFile, IntPtr.Zero, IntPtr.Zero, pLastWriteTime))
            throw new Exception();
    }
    finally
    {
        Marshal.FreeHGlobal(pLastWriteTime);
    }
}