Проблема с django-celery, не работающим в определенное время

У меня проблемы с тем, что django-celery не запускается в указанное время, но он всегда запускается каждую минуту. Ниже я вставил tasks.py, settings.py и celery.py. Я тестировал с djcelery, а также с сельдереем. Я использую сельдерейный бит.

celery.py (отредактировано, чтобы дать конкретную и избежать конфиденциальной информации.): -

from __future__ import absolute_import, unicode_literals

import os

from celery import Celery
from django.conf import settings
from celery.schedules import crontab
from datetime import timedelta



# set the default Django settings module for the 'celery' program.
os.environ.setdefault('DJANGO_SETTINGS_MODULE', 'netadc.settings')

app = Celery('netadc')
app.config_from_object(settings, namespace='CELERY')
app.autodiscover_tasks()

app = Celery('proj',
             broker='redis://',
             backend='redis://',
             include=['standalone.tasks'])



CELERY_BEAT_SCHEDULE = {
    "runs-every-30-seconds": {
        "task": "tasks.cron_span",
        "schedule": 30.0,
        "args": ()
    },
}

if __name__ == '__main__':
    app.start()

settings.py: -

# Application definition

INSTALLED_APPS = (
    'django.contrib.admin',
    'django.contrib.auth',
    'django.contrib.contenttypes',
    'django.contrib.sessions',
    'django.contrib.messages',
    'django.contrib.staticfiles',
    'home',
    'ivpn',
    'nsp',
    'lib',
    'ciscoaci',
    'standalone',
    'arista',
    'spa',
    'inet',
    #'django_countries',
    'djcelery',
    #'debug_toolbar',
    'celery',
    'django_celery_beat',
)

ROOT_URLCONF = 'netadc.urls'

TEMPLATES = [
    {
        'BACKEND': 'django.template.backends.django.DjangoTemplates',
        'DIRS': [],
        'APP_DIRS': True,
        'OPTIONS': {
            'context_processors': [
                'ivpn.context_processors.vpnreq_info',
                'django.template.context_processors.debug',
                'django.template.context_processors.request',
                #'django.core.context_processors.request',
                'django.contrib.auth.context_processors.auth',
                'django.contrib.messages.context_processors.messages',
            ],
        },
    },
]

WSGI_APPLICATION = 'netadc.wsgi.application'

# Internationalization
# https://docs.djangoproject.com/en/1.8/topics/i18n/

LANGUAGE_CODE = 'en-us'

#TIME_ZONE = 'UTC'
TIME_ZONE = 'America/Phoenix'

USE_TZ = True

## Celery specific settings
CELERY_BROKER_URL = 'redis://localhost:6379/0'
CELERYBEAT_SCHEDULER = 'djcelery.schedulers.DatabaseScheduler'
CELERY_RESULT_BACKEND = 'redis://'
CELERY_ACCEPT_CONTENT = ['json']
CELERY_TASK_SERIALIZER = 'json'
CELERY_RESULT_SERIALIZER = 'json'
CELERY_TIMEZONE = 'America/Phoenix'
CELERY_ENABLE_UTC = True

tasks.py: -

from __future__ import absolute_import, division, print_function
# -*- coding: utf-8 -*-
from __builtin__ import *
#from future.builtins.disabled import *
from django.template.context_processors import csrf
from django.http import Http404
from django.shortcuts import get_object_or_404,render
from django.http import HttpResponse, HttpResponseRedirect
from django.template import loader
# Create your views here.
from django.shortcuts import render
#from django.urls import 
from django.core.urlresolvers import reverse
import json
import os
import requests
import argparse
import collections
import datetime
from django.template import RequestContext
from standalone.forms import UploadFileForm
from django.contrib import messages
#import pyexcel.ext.xls
import urllib
import urllib2
import cookielib
import sys, getopt
import StringIO,contextlib
import xml.etree.ElementTree as ET
from standalone.views import *
from standalone.models import Fabric, Span
#from celery.decorators import task
from celery import task
from celery.utils.log import get_task_logger
from celery import shared_task
from celery.schedules import crontab
from celery.decorators import periodic_task
from time import time as time1
import time
from datetime import timedelta
import datetime

logger = get_task_logger(__name__)
@task()
def cron_span():
      ########### code #############################

Я изменил часовой пояс, чтобы он был одинаковым во всех местах, и я также обновил планировщик базы данных, используя команды: - from djcelery.models import PeriodicTask PeriodicTask.objects.update (last_run_at = None)

Любая помощь будет оценена.

поленья сельдерея: -

[2018-03-18 11:09:55,078: INFO/Beat] Writing entries...
[2018-03-18 11:10:00,001: INFO/Beat] Scheduler: Sending due task standalone.tasks.cron_span (standalone.tasks.cron_span)
[2018-03-18 11:10:00,003: INFO/MainProcess] Received task: standalone.tasks.cron_span[707c0da7-d76b-4c4d-92a4-3839f5cd6527]  
[2018-03-18 11:10:00,005: WARNING/ForkPoolWorker-2] where are we
[2018-03-18 11:10:00,011: WARNING/ForkPoolWorker-2] each_all_values
[2018-03-18 11:10:00,011: WARNING/ForkPoolWorker-2] <type 'datetime.datetime'>
[2018-03-18 11:10:00,011: WARNING/ForkPoolWorker-2] each_all_values.time_span
[2018-03-18 11:10:00,012: WARNING/ForkPoolWorker-2] <type 'float'>
[2018-03-18 11:10:00,012: WARNING/ForkPoolWorker-2] present_time
[2018-03-18 11:10:00,013: ERROR/ForkPoolWorker-2] Task standalone.tasks.cron_span[707c0da7-d76b-4c4d-92a4-3839f5cd6527] raised unexpected: ValueError('invalid literal for float(): 2018-03-12 21:22:05',)
Traceback (most recent call last):
  File "/root/.venvs/netadc/lib/python2.7/site-packages/celery-4.1.0-py2.7.egg/celery/app/trace.py", line 374, in trace_task
    R = retval = fun(*args, **kwargs)
  File "/root/.venvs/netadc/lib/python2.7/site-packages/celery-4.1.0-py2.7.egg/celery/app/trace.py", line 629, in __protected_call__
    return self.run(*args, **kwargs)
  File "/apps/workspace/netadc/standalone/tasks.py", line 57, in cron_span
    time_taken = present_time - float(each_all_values.time_span.strftime("%Y-%m-%d %H:%M:%S")) # time_taken is in seconds
ValueError: invalid literal for float(): 2018-03-12 21:22:05



[2018-03-18 11:11:00,001: INFO/Beat] Scheduler: Sending due task standalone.tasks.cron_span (standalone.tasks.cron_span)
[2018-03-18 11:11:00,004: INFO/MainProcess] Received task: standalone.tasks.cron_span[23928119-c93a-41c5-9bc7-e2c909324b6f]  
[2018-03-18 11:11:00,005: WARNING/ForkPoolWorker-5] where are we
[2018-03-18 11:11:00,012: WARNING/ForkPoolWorker-5] each_all_values
[2018-03-18 11:11:00,012: WARNING/ForkPoolWorker-5] <type 'datetime.datetime'>
[2018-03-18 11:11:00,012: WARNING/ForkPoolWorker-5] each_all_values.time_span
[2018-03-18 11:11:00,012: WARNING/ForkPoolWorker-5] <type 'float'>
[2018-03-18 11:11:00,013: WARNING/ForkPoolWorker-5] present_time
[2018-03-18 11:11:00,014: ERROR/ForkPoolWorker-5] Task standalone.tasks.cron_span[23928119-c93a-41c5-9bc7-e2c909324b6f] raised unexpected: ValueError('invalid literal for float(): 2018-03-12 21:22:05',)
Traceback (most recent call last):
  File "/root/.venvs/netadc/lib/python2.7/site-packages/celery-4.1.0-py2.7.egg/celery/app/trace.py", line 374, in trace_task
    R = retval = fun(*args, **kwargs)
  File "/root/.venvs/netadc/lib/python2.7/site-packages/celery-4.1.0-py2.7.egg/celery/app/trace.py", line 629, in __protected_call__
    return self.run(*args, **kwargs)
  File "/apps/workspace/netadc/standalone/tasks.py", line 57, in cron_span
    time_taken = present_time - float(each_all_values.time_span.strftime("%Y-%m-%d %H:%M:%S")) # time_taken is in seconds
ValueError: invalid literal for float(): 2018-03-12 21:22:05