If you apply INLAND, and have legal status in Canada when you send in your application, you can send in for an open work permit at the same time. If you've already applied and satisfy those two requirements, you can apply any time. Wait time seems to be 2-4 months, and I think the permits last for 2 years but that might be on a case-by-case basis.
If you don't have legal status in Canada, you have to wait for AIP (15 months?).
If you applied outland, you have to wait (even if you live in Canada), unless you are 30 or under and try for a working holiday or equivalent visa, depending on your country of citizenship.