This is something i made quick to get a feel of how a monitor with a certain input lag would feel like.

Latency Simulator.py

import pygame

pygame.init()
pygame.display.set_caption("Mouse Latency Simulator - by pbsds")
pygame.font.init()
window = pygame.display.set_mode((1280, 720))
font = pygame.font.Font(None, 20)

pygame.mouse.set_visible(False)

delayedMouse = []
latency = 40#ms
latency_Spr = font.render("%ims latency" % latency, False, (255, 255, 255))
mouse = [0, 0]

while 1:
	tick = pygame.time.get_ticks()
	update = False
	
	events = pygame.event.get()
	for i in events:
		if i.type == pygame.MOUSEMOTION:
			delayedMouse.append((tick + latency, i.pos))
		elif i.type == pygame.MOUSEBUTTONDOWN:
			if i.button == 4:
				latency += 1
			elif i.button == 5:
				if latency >= 1: latency -= 1
			else: continue
			latency_Spr = font.render("%ims latency" % latency, False, (255, 255, 255))
			update = True
		elif i.type == pygame.QUIT:
			sys.exit()
	
	while len(delayedMouse):
		if delayedMouse[0][0] < tick:
			mouse = delayedMouse.pop(0)[1]
			update = True
		else:
			break
	
	if update:
		window.fill((0, 0, 0))
		window.blit(latency_Spr, (0, 0))
		pygame.draw.rect(window, (255, 255, 255), (mouse[0], mouse[1], 10, 10))
		pygame.display.flip()