Android : System thread inside a Timer in Android

So I have a Timer in my Activity and I want to run that every 10 seconds.

I created a System.Threading.Timer:

timer = new Timer ((o) => {
    Action syncAct = new Action (async delegate() {
        await FetchData();
    });

    RunOnUiThread (syncAct);
}, null, 0, 10000);

The problem here is that await FetchData() takes longer than 10 seconds and that causes the timer to go on forever. I need the timer to start every time AFTER the sync completes. How can I do that?

Thank you for your time.