How should I schedule my task in django
Basically you can use Celery's preiodic tasks with expire option, which makes you sure that your tasks will not be executed twice. 
Also you could run your own script with infinite loop like which will run calculation. If your calculation will run more than minute you can spawn your tasks using eventlet or gevent. Other option you could creare celery-tasks from this script and be sure that your tasks executes every N seconds, as you prefer.
In my django project, I need to collect data from about 50 remote servers into the local database minutely or every 30-seconds. Though it works with crontab in the remote servers, I want to do this in the project. Firstly, I consider the django-celery. However it does well in asynchronous processing and the collect-data task could not be delayed. Therefore i think, it may be not fit.  How if i do this use the timer for python  and what need i to pay more attention.  Excuse for my ignorance of python and django. I'll appreciate other advice or ideas. Many thanks