How to add objects to ArrayList one at a time at timed intervals

Processing Coding Questions
2

Full code if anyone needs it (pretty messy):



int cols, rows;
int scl = 20;
int w = 2000;
int h = 1600;
Ship ship;
Ground ground;
ArrayList<Spikes> spikes;
color g;
color s;
float flying = 0;
float score = 0;
float[][] terrain;
boolean gameStart;
boolean gameOver;

void setup() {
  size(600, 600, P3D);
  cols = w / scl;
  rows = h/ scl;
  terrain = new float[cols][rows];
  g = color(156,111,81);
  s = color(0);
  ship = new Ship(1000,1100,200);
  ground = new Ground(1000,1100,200);
  spikes = new ArrayList<Spikes>();
  gameStart = true;
  gameOver = false;
}


void draw() {
  if( gameStart == true){
  flying -= 0.1;
  
  
  for (int y = 0; y < rows; y++) {
    for (int x = 0; x < cols; x++) {
       terrain[x][y] = flying;
    }
  } 



  background(0);
  textSize(50);
  fill(255);
  text(score, 50,50);
  stroke(s);
  fill(g);
  score += 0.01;
  translate(width/2, height/2+50);
  rotateX(PI/3);
  translate(-w/2, -h/2);
  ground.render();
  for (int y = 0; y < rows-1; y++) {
    beginShape(TRIANGLE_STRIP);
    for (int x = 0; x < cols; x++) {
      vertex(x*scl, y*scl, terrain[x][y]);
      vertex(x*scl, (y+1)*scl, terrain[x][y+1]);
      
    }
    endShape();
    // Idea for terrain using a triangle sector adapted from The Coding Train by Dan Shiffman
  }
  if(score > 0 && score < 25){
    spikes.add(new Spikes(width/2,500,50));
    
  }
  for(int i=0; i < spikes.size(); i++){
    spikes.get(i).render();
     spikes.get(i).move();
  }
  ship.render();
  ship.move();
  }
}

class Ship{
  float x;
  float y;
  float z;
 
  
  Ship(float _x, float _y, float _z){
    x = _x;
    y = _y;
    z = _z;
  }
  void render(){
    translate(x,y,z);
    fill(160);
    stroke(0);
    
     beginShape(TRIANGLES);
     scale(0.6);
      vertex(-50,0,25);
      vertex(-150,100,25);
      vertex(0,100,25);
      
      vertex(50,0,25);
      vertex(150,100,25);
      vertex(0,100,25);
      
       vertex(-50,0,-25);
      vertex(-150,100,-25);
      vertex(0,100,-25);
      
      vertex(50,0,-25);
      vertex(150,100,-25);
      vertex(0,100,-25);
      
      vertex(-50,0,25);
      vertex(50,0,25);
      vertex(0,-300,25);
      
      vertex(-50,0,25);
      vertex(50,0,25);
      vertex(0,100,25);
      
      vertex(-150,100,25);
      vertex(150,100,25);
      vertex(-150,100,-25);
      
      vertex(150,100,25);
      vertex(-150,100,-25);
      vertex(150,100,-25);
      
       vertex(-150,100,25);
      vertex(150,100,25);
      vertex(150,100,-25);
      
       vertex(50,0,25);
       vertex(50,0,-25);
        vertex(0,-300,-25);
        
        vertex(50,0,25);
       vertex(0,-300,25);
        vertex(0,-300,-25);
        
        vertex(-50,0,25);
       vertex(-50,0,-25);
        vertex(0,-300,-25);
        
        vertex(-50,0,25);
       vertex(0,-300,25);
        vertex(0,-300,-25);
       
        vertex(-50,0,25);
      vertex(-50,0,-25);
      vertex(-150,100,25);
      
        vertex(50,0,25);
      vertex(50,0,-25);
      vertex(150,100,25);
      
endShape(); 
  }
  void move(){
    if(keyPressed && keyCode == LEFT){
      x-=3;
    }
     if(keyPressed && keyCode == RIGHT){
      x+=3;
    }
     if(keyPressed && keyCode == UP){
      y-=3;
    }
     if(keyPressed && keyCode == DOWN){
      y+=3;
    }
  }
}
class Ground{
  float x;
  float y;
  float z;
  Ground(float _x,float _y,float _z){
    x = _x;
    y = _y;
    z = _z;
  }
  void render(){
    fill(g);
    translate(x,y,z);
    beginShape(TRIANGLES);
    
    vertex(100,100,2000);
      vertex(100,2000,-150);
      vertex(100,100,-150);
      translate(-x,-y,-z);
      endShape();
  }
}
class Spikes{
  float x;
  float y;
  float z;
 
  
  Spikes(float _x, float _y, float _z){
    x = _x;
    y = _y;
    z = _z;
  }
  void render(){
    translate(x,y,z);
    fill(0);
    stroke(255);
   
    beginShape(TRIANGLES);
    
    vertex(100,-300,-100);
    vertex(150,-350,-100);
    vertex(100,-300,200);
    
    vertex(100,-300,-100);
    vertex(50,-350,-100);
    vertex(100,-300,200);
    
    endShape();
   translate(-x,-y,-z);
   
  }
  void move(){
    y+=4;
    if(y>1810){
      x = random(300,1500);
      y = 600;
    }
  }
}