Make something happen if a specific time is left on DispatcherTimer

Question

I'm currently working on a UWP project and need some help with my DispatcherTimer.

What I'm working with is a booking function and I want a color to change if there is 15 seconds left until the DispatcherTimer ticks.

I have two variables that is named timefrom and timeTo and they come from a SQL database. So what I want to do is to first change a color from Green to Red and then stay Red until there is 15 seconds left until the timeto = DateTime.UtcNow

"timefrom": "2018-02-17T14:00:00"
"timeto": "2018-02-17T15:15:00"

Right now, what I have tried with is this:

if (timeto < DateTime.UtcNow)
{
    StatusColor.Fill = GreenBrush;
}
else if (timeto > DateTime.UtcNow)
{
    GreenToRed();
}

This is my DispatcherTimer:

public void GreenToRed()
        {
            DispatcherTimer ColorTimer = new DispatcherTimer();
            ColorTimer.Interval = TimeSpan.FromSeconds(3);
            ColorTimer.Tick += async (Sender, args) =>
            {
                await StatusColor.Fade(duration: 1000, delay: 0, value: 0).StartAsync();
                StatusColor.Fill = RedBrush;
                await StatusColor.Fade(duration: 1200, delay: 0, value: 1).StartAsync();
                RedToYellow();
                ColorTimer.Stop();
            };
            ColorTimer.Start();
        }

• StatusColor is a retangle that is suposed to contain the color as a fill.
• GreenBrush, RedBrush and YellowBrush is the three colors that I want to switch between.

Thanks in advance!