Check if the countdown timer is 0

I have a script based on the countdown timer. I want that when the time reaches 0, the timer stop and a message appear. The code id this:

public partial class simulare : Form
    {
        private admin admin;
        Timer timer = new Timer();
        public simulare(admin admin)
        {
            InitializeComponent();
            this.admin=admin;
            label2.Text = TimeSpan.FromMinutes(0.1).ToString();
        }
        private void simulare_Load(object sender, EventArgs e)
        {
            var startTime = DateTime.Now;
            timer = new Timer() { Interval = 1000 };
            timer.Tick += (obj, args) =>
            label2.Text = (TimeSpan.FromMinutes(0.1) - (DateTime.Now - startTime)).ToString("hh\\:mm\\:ss");
            timer.Enabled = true;
            timer.Start();
            if (condition)
            {
                timer.Stop();
                MessageBox.Show("Done!");
            }
        }
    }

I tried those conditions, but unsuccessful:

if (timer.ToString() == TimeSpan.Zero.ToString())

if (label2.Text.ToString() == TimeSpan.Zero.ToString())

if (label2.Text == TimeSpan.Zero)