How to make the screen visible for 20 seconds or more in the Xamarin forms

Hi I have 3 content pages here

first.cs
second.cs
third.cs

In First.cs I have following code snippet.

Button b=new Button(){
Title="Submit"
};
b.clicked+=(){

//Here I would like to call the second page to display for 20 sec
//then display thrid page
Navigation.pushAync( new Third);
};

Second.cs

This content page contain only a text Label like

"Please wait do not refresh or click on the back button"

How can I do that Please comment !!!!!!!!!!!!!!!!!