用python实现：抽奖时段为每周六 23:00~23:40，每 20 分钟开奖一次，共 3 轮。

可以使用datetime和time模块来实现该功能。

首先，需要获取当前的日期和时间：

import datetime
now = datetime.datetime.now()

然后，判断当前是否为周六，并且时间是否在23:00~23:40之间：

if now.weekday() == 5 and now.hour == 23 and now.minute >= 0 and now.minute <= 40:
    # 进行抽奖
else:
    # 不在抽奖时间段

接下来，需要根据当前时间计算出距离开奖还有多少秒：

delta = datetime.timedelta(minutes=20)
start_time = datetime.datetime(now.year, now.month, now.day, 23, 0)
round1_end_time = start_time + delta
round2_end_time = round1_end_time + delta
round3_end_time = round2_end_time + delta

if now >= start_time and now < round1_end_time:
    # 第一轮抽奖
    seconds_left = (round1_end_time - now).total_seconds()
elif now >= round1_end_time and now < round2_end_time:
    # 第二轮抽奖
    seconds_left = (round2_end_time - now).total_seconds()
elif now >= round2_end_time and now < round3_end_time:
    # 第三轮抽奖
    seconds_left = (round3_end_time - now).total_seconds()
else:
    # 不在抽奖时间段

最后，可以使用time模块的sleep函数来等待开奖：

import time

# 等待开奖
time.sleep(seconds_left)

# 进行开奖操作

完整代码如下：

import datetime
import time

now = datetime.datetime.now()

if now.weekday() == 5 and now.hour == 23 and now.minute >= 0 and now.minute <= 40:
    delta = datetime.timedelta(minutes=20)
    start_time = datetime.datetime(now.year, now.month, now.day, 23, 0)
    round1_end_time = start_time + delta
    round2_end_time = round1_end_time + delta
    round3_end_time = round2_end_time + delta

    if now >= start_time and now < round1_end_time:
        # 第一轮抽奖
        seconds_left = (round1_end_time - now).total_seconds()
    elif now >= round1_end_time and now < round2_end_time:
        # 第二轮抽奖
        seconds_left = (round2_end_time - now).total_seconds()
    elif now >= round2_end_time and now < round3_end_time:
        # 第三轮抽奖
        seconds_left = (round3_end_time - now).total_seconds()
    else:
        # 不在抽奖时间段
        seconds_left = 0

    # 等待开奖
    time.sleep(seconds_left)

    # 进行开奖操作
else:
    # 不在抽奖时间段