Timed Object Generation For Guitar Hero Game

I want to generate a new tile every 1,5,10,15 (please check the code to gain an understanding of where I'm going) the session last for 4m :20 sec, I need using the date package, I tried using the sleep method however I don't want to pause the whole thread, so I need setting up the time aspect of the key generation (assume all other code works).

Java Code:

import info.gridworld.actor.*;
import info.gridworld.grid.*;
import java.awt.*;
import java.util.*;
//importations, just in case you were wondering
//locations and actor world are set up
//assume all other code works

[Code] ....

I'm using grid world to set up the locations, the tiles are actors that move south every turn