According to new support documents, Telus is expecting to push the upcoming Android Marshmallow update to both the Nexus 5 and Nexus 6 beginning October 5. Google is hosting an event on September 29, in which it will likely reveal new hardware, along with more information about the release of the new OS. The carrier notes that the dates are subject to change, though with Google's generally quick release of the OS, the timeline isn't too far fetched.
On September 29, Google is expected to make both the Nexus 5X and Nexus 6P official, which will both launch running the new version of Android. It won't be long before we know the official release plans, so keep it locked to Android Central for full coverage of the event and announcements.