Build a context first with setSite()
, and perhaps a request object:
from zope.app.component.hooks import setSite
from Testing.makerequest import makerequest
app = makerequest(app)
site = app[site_id]
setSite(site)
This does require that you open a ZODB connection yourself and traverse to the site object yourself.
However, it is not clear how you are accessing the Plone site from your scheduler. Instead of running a full new Zope process, consider calling a URL from your scheduling job. If you integrated APScheduler into your Zope process, you'd have to create a new ZODB connection in the job, traverse to the Plone site from the root, and use the above method to set up the site hooks (needed for a lot of local components anyway).