private int timeRemaining;
private boolean gameOver;

public void setTimeRemaining(int duration)
{
    timeRemaining = duration;
    gameOver = false;
}

public void act()
{
    if (gameOver) return;
    //everything else world does
    if (timeRemaining > 0 && --timeRemaining == 0) gameOver();
}

private void gameOver()
{
    gameOver = true;
    // whatever else you want to do when ending a game
}

((MyWorld)getWorld()).setTimeRemaining(3600);

public class SimpleActor extends greenfoot.Actor {}

private Actor timerDisplay = new SimpleActor();

private void updateTimerDisplay()
{
    GreenfootImage img = new GreenfootImage("Time left: "+timeRemaining, 32, Color.BLACK, new Color(0, 0, 0, 0));
    timerDisplay.setImage(img);
}

updateTimerDisplay();
addObject(timerDisplay, 150, 15);

updateTimerDisplay();

public class easyButton extends Actor
{
    public int time = 3600;
    // constructor
    
    public easyButton(){
    GreenfootImage myImage = getImage();
       int myNewH = (int)myImage.getHeight()/6;
       int myNewW = (int)myImage.getWidth()/6;
       myImage.scale(myNewW, myNewH);
    }
    /**
     * Act - do whatever the easyButton wants to do. This method is called whenever
     * the 'Act' or 'Run' button gets pressed in the environment.
     */
    public void act()
    {
        
        if(Greenfoot.mouseClicked(this)){
            ((MyWorld)getWorld()).setTimeRemaining(3600);
            Greenfoot.setWorld(new MyWorld());
        }
    }
    
}

public class easyButton extends Actor
{
    //public int time = 3600;
    MyWorld timer = new MyWorld();
    // constructor
    
    public easyButton(){
    GreenfootImage myImage = getImage();
       int myNewH = (int)myImage.getHeight()/6;
       int myNewW = (int)myImage.getWidth()/6;
       myImage.scale(myNewW, myNewH);
    }
    /**
     * Act - do whatever the easyButton wants to do. This method is called whenever
     * the 'Act' or 'Run' button gets pressed in the environment.
     */
    public void act()
    {
        
        if(Greenfoot.mouseClicked(this)){
            timer.setTimeRemaining(4800);
            Greenfoot.setWorld(new MyWorld());
        }
    }
    
}

if (timer > 0) {
            timer--;
            if (timer%60 == 0){
            timerText.setText("Time Left: " + (timer/60));
            }
            if(timer == 0) {
                Greenfoot.stop();
            }
        }

public void act()
{
    if (Greenfoot.mouseClicked(this))
    {
        MyWorld mw = new MyWorld();
        mw.setTimeRemaining(time);
        Greenfoot.setWorld(mw);
    }
}