Counting time in pygame

I want to count time in pygame, when an event occurs. Ive read something in the documentation but I dont really understand on how to do it.

In the documentation you can get time in miliseconds but it starts counting when the pygame.init() is called. I want to count from 0 when the boolean is true.

import pygame
pygame.init()

loop = True

boolean = False

while loop:
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            pygame.quit()
            quit()
        if event.type == pygame.KEYDOWN:
            if event.key == pygame.RETURN:
                boolean = True

     screen.fill((255, 255, 255))

     if boolean:
        # start counting seconds

     pygame.display.update()

Thanks for your time.