In Python, how can I put a thread to sleep until a specific time?

Here's a half-ass solution that doesn't account for clock jitter or adjustment of the clock. See comments for ways to get rid of that.

import time
import datetime

# if for some reason this script is still running
# after a year, we'll stop after 365 days
for i in xrange(0,365):
    # sleep until 2AM
    t = datetime.datetime.today()
    future = datetime.datetime(t.year,t.month,t.day,2,0)
    if t.hour >= 2:
        future += datetime.timedelta(days=1)
    time.sleep((future-t).total_seconds())
    
    # do 2AM stuff

One possible approach is to sleep for an hour. Every hour, check if the time is in the middle of the night. If so, proceed with your operation. If not, sleep for another hour and continue.

If the user were to change their clock in the middle of the day, this approach would reflect that change. While it requires slightly more resources, it should be negligible.

Another approach, using sleep, decreasing the timeout logarithmically.

def wait_until(end_datetime):
    while True:
        diff = (end_datetime - datetime.now()).total_seconds()
        if diff < 0: return       # In case end_datetime was in past to begin with
        time.sleep(diff/2)
        if diff <= 0.1: return

Building on the answer of @MZA and the comment of @Mads Y

Slightly more generalized solution (based off of Ross Rogers') in case you'd like to add minutes as well.

def sleepUntil(self, hour, minute):
    t = datetime.datetime.today()
    future = datetime.datetime(t.year, t.month, t.day, hour, minute)
    if t.timestamp() > future.timestamp():
        future += datetime.timedelta(days=1)
    time.sleep((future-t).total_seconds())

adapt this:

from datetime import datetime, timedelta
from time import sleep

now = datetime.utcnow
to = (now() + timedelta(days = 1)).replace(hour=1, minute=0, second=0)
sleep((to-now()).seconds)

Asynchronous version of Omrii's solution

import datetime
import asyncio

async def sleep_until(hour: int, minute: int, second: int):
    """Asynchronous wait until specific hour, minute and second

    Args:
        hour (int): Hour
        minute (int): Minute
        second (int): Second

    """
    t = datetime.datetime.today()
    future = datetime.datetime(t.year, t.month, t.day, hour, minute, second)
    if t.timestamp() > future.timestamp():
        future += datetime.timedelta(days=1)
    await asyncio.sleep((future - t).total_seconds())

I know is way late for this, but I wanted to post an answer (inspired on the marked answer) considering systems that might have - incorrect - desired timezone + include how to do this threaded for people wondering how.

It looks big because I'm commenting every step to explain the logic.

import pytz #timezone lib
import datetime
import time
from threading import Thread

# using this as I am, check list of timezone strings at:
## https://en.wikipedia.org/wiki/List_of_tz_database_time_zones
TIMEZONE = pytz.timezone("America/Sao_Paulo")

# function to return desired seconds, even if it's the next day
## check the bkp_time variable (I use this for a bkp thread)
## to edit what time you want to execute your thread
def get_waiting_time_till_two(TIMEZONE):
    # get current time and date as our timezone
    ## later we remove the timezone info just to be sure no errors
    now = datetime.datetime.now(tz=TIMEZONE).replace(tzinfo=None)
    curr_time = now.time()
    curr_date = now.date()

    # Make 23h30 string into datetime, adding the same date as current time above
    bkp_time = datetime.datetime.strptime("02:00:00","%H:%M:%S").time()
    bkp_datetime = datetime.datetime.combine(curr_date, bkp_time)

    # extract the difference from both dates and a day in seconds
    bkp_minus_curr_seconds = (bkp_datetime - now).total_seconds()
    a_day_in_seconds = 60 * 60 * 24

    # if the difference is a negative value, we will subtract (- with + = -)
    # it from a day in seconds, otherwise it's just the difference
    # this means that if the time is the next day, it will adjust accordingly
    wait_time = a_day_in_seconds + bkp_minus_curr_seconds if bkp_minus_curr_seconds < 0 else bkp_minus_curr_seconds

    return wait_time

# Here will be the function we will call at threading
def function_we_will_thread():
    # this will make it infinite during the threading
    while True:
        seconds = get_waiting_time_till_two(TIMEZONE)
        time.sleep(seconds)
        # Do your routine

# Now this is the part where it will be threading
thread_auto_update = Thread(target=function_we_will_thread)
thread_auto_update.start()

It takes only one of the very basic libraries.

import time

sleep_until = 'Mon Dec 25 06:00:00 2020' # String format might be locale dependent.
print("Sleeping until {}...".format(sleep_until))
time.sleep(time.mktime(time.strptime(sleep_until)) - time.time())

• time.strptime() parses the time from string -> struct_time tuple. The string can be in different format, if you give strptime() parse-format string as a second argument. E.g. time.strptime("12/25/2020 02:00AM", "%m/%d/%Y %I:%M%p")
• time.mktime() turns the struct_time -> epoch time in seconds.
• time.time() gives current epoch time in seconds.
• Substract the latter from the former and you get the wanted sleep time in seconds.
• sleep() the amount.

If you just want to sleep until whatever happens to be the next 2AM, (might be today or tomorrow), you need an if-statement to check if the time has already passed today. And if it has, set the wake up for the next day instead.

import time

sleep_until = "02:00AM" # Sets the time to sleep until.

sleep_until = time.strftime("%m/%d/%Y " + sleep_until, time.localtime()) # Adds todays date to the string sleep_until.
now_epoch = time.time() #Current time in seconds from the epoch time.
alarm_epoch = time.mktime(time.strptime(sleep_until, "%m/%d/%Y %I:%M%p")) # Sleep_until time in seconds from the epoch time.

if now_epoch > alarm_epoch: #If we are already past the alarm time today.
    alarm_epoch = alarm_epoch + 86400 # Adds a day worth of seconds to the alarm_epoch, hence setting it to next day instead.

time.sleep(alarm_epoch - now_epoch) # Sleeps until the next time the time is the set time, whether it's today or tomorrow.

Instead of using the wait() function, you can use a while-loop checking if the specified date has been reached yet:

if datetime.datetime.utcnow() > next_friday_10am:
    # run thread or whatever action
    next_friday_10am = next_friday_10am()
    time.sleep(30)

def next_friday_10am():
    for i in range(7):
        for j in range(24):
            for k in range(60):
                if (datetime.datetime.utcnow() + datetime.timedelta(days=i)).weekday() == 4:
                    if (datetime.datetime.utcnow() + datetime.timedelta(days=i, hours=j)).hour == 8:
                        if (datetime.datetime.utcnow() + datetime.timedelta(days=i, hours=j, minutes=k)).minute == 0:
                            return datetime.datetime.utcnow() + datetime.timedelta(days=i, hours=j, minutes=k)

Still has the time-checking thread check the condition every after 30 seconds so there is more computing required than in waiting, but it's a way to make it work.