我想暂停所有的请求一段时间，一旦我的爬虫程序运行到超过当前计时器20秒的时间，然后让它像往常一样继续运行直到完成。
我发现我当前的脚本没有实现暂停，蜘蛛照常继续，我如何使它有效地工作？

import scrapy
from scrapy import signals
import datetime
from twisted.internet import defer
from twisted.internet import defer
class TestSpider(scrapy.Spider):
    name = 'signal'

    start_urls = start_urls = [f'https://www.meadowhall.co.uk/eatdrinkshop?page={i}' for i in range(1, 15)]

    custom_settings = {
        'DOWNLOAD_DELAY':2
    }

    def __init__(self):
        self.timer = 0
        self.datetime = datetime.datetime.now()

    @classmethod
    def from_crawler(cls, crawler, *args,**kwargs):
        spider = super(TestSpider, cls).from_crawler(crawler, *args,**kwargs)
        crawler.signals.connect(spider.schedule_request, signal=signals.request_scheduled)
        crawler.signals.connect(spider.close_spider, signal=signals.spider_closed)
        return spider

    def schedule_request(self):
        self.timer += 1
        if self.datetime == (self.datetime + datetime.timedelta(seconds = 20)).time():
            deferred = defer.Deferred()
            deferred.pause(self.timer)
            deferred.unpause()

    def close_spider(self):
        print(f"The current time: {datetime.datetime.now().time()}")

    def start_requests(self):
        for url in self.start_urls:
            yield scrapy.Request(
                url=url,
                callback=self.parse,
                cb_kwargs = {
                    'pg':url
                }
            ) 
    def parse(self, response,pg):
        content_page = response.xpath("//div[@class='view-content']//div")
        url_split = pg.split('?')[-1]
        for cnt in content_page:
            image_url = cnt.xpath(".//img//@src").get()
            if image_url != None:
                yield {
                    'image_urls':image_url,
                    'url_page':url_split
                }