Windows Forms, Timer calling event when timer starts

Question

I'm trying to create a timed task program (think Reminders app for Apple but with timers), and I'm trying to implement the timer. The timer starts and the event works fine, but for some reason, the timer event gets called right after starting the timer, rather than after the specified interval. This is my code for setting the interval:

 newTask.timerTime = float.Parse(timeInput.Text);

newTask.Initialize();
switch (timeInput.Text)
{
    case "Seconds":
        newTask.timer.Interval = (int)newTask.timerTime * 1000;
        break;
    case "Minutes":
        newTask.timer.Interval = (int)(newTask.timerTime * 1000) * 60;
        break;
    case "Hours":
        newTask.timer.Interval = (int)((newTask.timerTime * 1000) * 60) * 60;
        break;
}
newTask.timer.Enabled = true;
newTask.timer.Start();

And this is my code for creating the event (and Timer.Tick):

public void Initialize()
{
    timer.Tick += new System.EventHandler(OnTimerEnd);
}

//Timer event
private void OnTimerEnd(object sender, EventArgs e)
{
    new ToastContentBuilder()
        .AddArgument("action", "viewConversation")
        .AddArgument("taskid", 1)
        .AddText("Your timer is up!")
        .AddText($@"Your task, {taskName}, is now completed! Great job!")
        .Show();

    timer.Stop();
    timer.Enabled = false;
}