Google has been testing Android 6.0 over the summer, and you might have even been running the developer previews, but when is the final version rolling out? We've been able to confirm that the rollout is scheduled to start on October 5th, which is the date previously leaked in a Telus FAQ page.
As with all of Google's updates, you can expect the process to be slow if you wait for the OTA. The update ZIP will probably be located quickly, though, allowing you to manually update. There will also be factory images available if you need to flash back to stock or are rooted. October 5th is when the final Marshmallow code will be pushed to AOSP too.
We can also confirm once and for all that Android 6.0 is not going to be coming to the Nexus 4, 7 (2012), and 10. They'll stay on Lollipop forever. It's not a matter of whether the hardware could technically run 6.0, but if it's worth the time and effort it would take to support a device from 2012.