How to display an image after a time interval?

Start the timer when the user clicks a mouse button, then calculate the passed time in the main loop and if it's >= 3, blit the image.

import pygame as pg


def main():
    screen = pg.display.set_mode((640, 480))
    clock = pg.time.Clock()
    font = pg.font.Font(None, 40)
    img = pg.Surface((100, 100))
    img.fill((190, 140, 50))
    click_time = 0
    passed_time = 0

    done = False

    while not done:
        for event in pg.event.get():
            if event.type == pg.QUIT:
                done = True
            # Start the timer.
            elif event.type == pg.MOUSEBUTTONDOWN:
                click_time = pg.time.get_ticks()

        screen.fill((30, 30, 30))
        if click_time != 0:  # If timer has been started.
            # Calculate the passed time since the click.
            passed_time = (pg.time.get_ticks()-click_time) / 1000

        # If 3 seconds have passed, blit the image.
        if passed_time >= 3:
            screen.blit(img, (50, 70))

        txt = font.render(str(passed_time), True, (80, 150, 200))
        screen.blit(txt, (50, 20))

        pg.display.flip()
        clock.tick(30)


if __name__ == '__main__':
    pg.init()
    main()
    pg.quit()