You can add this call inside your loop:
System.Threading.Thread.Sleep(5000); // 5,000 ms
or preferable for better readability:
System.Threading.Thread.Sleep(TimeSpan.FromSeconds(5));
However, if your application has a user interface you should never sleep on the foreground thread (the thread that processes the applications message loop).
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…