How to spawn and track multiple random objects with time delay in pygame?

I wonder how I can spawn objects (like an enemy) at a random position with a 2 seconds delay/cooldown.

I know how to spawn them at a random coordinate. But what I'm wondering is how I can spawn multiple objects and still keep track of the other ones that are already moving, kind of like you do when you shoot bullets in a pygame.

Here is the basic part that in this example spawns an asteroid. This works fine but how can I do it with multiple asteroids and keep track of them.

class Enemy:
    asteroids = [pygame.image.load('rock0.png'), pygame.image.load('rock1.png'), pygame.image.load('rock2.png'),
                 pygame.image.load('rock3.png'), pygame.image.load('rock4.png')]

    def __init__(self, y, width, height):
        self.width = width
        self.height = height
        self.vel = 1.5
        self.x = random.randrange(screen_width - self.width * 2)
        self.y = y
        self.asteroid = random.choice(self.asteroids)

    def draw(self, win):
        self.move()
        win.blit(self.asteroid, (self.x, self.y))

    def move(self):
        self.y = self.y + self.vel

Here is the entire code for anybody who needs it.

import pygame

import random

pygame.init()

screen_width = 500
screen_height = 500
win = pygame.display.set_mode((screen_width, screen_height))
walk_left = [pygame.image.load('sprite_5.png'), pygame.image.load('sprite_6.png')]
walk_right = [pygame.image.load('sprite_3.png'), pygame.image.load('sprite_4.png')]
standing = [pygame.image.load('sprite_0.png'), pygame.image.load('sprite_1.png'), pygame.image.load('sprite_2.png')]


class Player:
    def __init__(self, x, y, width, height):
        self.x = x
        self.y = y
        self.width = width
        self.height = height
        self.vel = 4
        self.left = False
        self.right = False
        self.standing = True
        self.walk_count = 0
        self.hitbox = (self.x, self.y - 30, 29, 52)

    def draw(self, win):
        if self.walk_count + 1 >= 12:
            self.walk_count = 0

        if not self.standing:
            if self.left:
                win.blit(walk_left[self.walk_count // 6], (self.x, self.y))
                self.walk_count += 1
            elif self.right:
                win.blit(walk_right[self.walk_count // 6], (self.x, self.y))
                self.walk_count += 1
        else:
            win.blit(standing[self.walk_count // 4], (self.x, self.y))
            self.walk_count += 1
        self.hitbox = (self.x + 2, self.y + 26, 123, 45)
        pygame.draw.rect(win, (255, 0, 0), self.hitbox, 2)


def move():
    if keys[pygame.K_LEFT] and man.x > man.vel or keys[pygame.K_a] and man.x > man.vel:
        man.x -= man.vel
        man.left = True
        man.right = False
        man.standing = False

    elif keys[pygame.K_RIGHT] and man.x < 500 - man.width - man.vel:
        man.x += man.vel
        man.left = False
        man.right = True
        man.standing = False

    else:
        man.standing = True


class Enemy:
    asteroids = [pygame.image.load('rock0.png'), pygame.image.load('rock1.png'), pygame.image.load('rock2.png'),
                 pygame.image.load('rock3.png'), pygame.image.load('rock4.png')]

    def __init__(self, y, width, height):
        self.width = width
        self.height = height
        self.vel = 1.5
        self.x = random.randrange(screen_width - self.width * 2)
        self.y = y
        self.asteroid = random.choice(self.asteroids)

    def draw(self, win):
        self.move()
        win.blit(self.asteroid, (self.x, self.y))

    def move(self):
        self.y = self.y + self.vel

class Projectile:
    def __init__(self, x, y, width, height, color):
        self.x = x
        self.y = y
        self.width = width
        self.height = height
        self.color = color
        self.vel = 5

    def draw(self, win):
        pygame.draw.rect(win, self.color, (self.x, self.y, self.height, self. width))


class Unit:
    def __init__(self):
        self.last = pygame.time.get_ticks()
        self.cooldown = 200

    def fire(self):
        now = pygame.time.get_ticks()
        if now - self.last >= self.cooldown:
            self.last = now
            spawn_bullet()


def spawn_bullet():
    if keys[pygame.K_SPACE]:
        bullets.append(Projectile((man.x + man.width // 2), (man.y - 7), 7, 3, (255, 0, 0)))


def re_draw():
    win.fill((0, 0, 0))
    asteroid.draw(win)
    man.draw(win)
    for bullet in bullets:
        bullet.draw(win)
    pygame.display.update()


delay = Unit()
man = Player(186, 400, 128, 128)
bullets = []
asteroid = Enemy(10, 64, 64)
run = True
clock = pygame.time.Clock()
while run:
    last = pygame.time.get_ticks()
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            run = False

    for bullet in bullets:
        if 0 < bullet.y < 500:
            bullet.y -= bullet.vel
        else:
            bullets.pop(bullets.index(bullet))

    keys = pygame.key.get_pressed()
    move()
    delay.fire()
    clock.tick(60)
    re_draw()

pygame.quit()