Not sure how helpful this will be to anyone, or if this is standard practice and I'm not telling you anything you don't know.... but if like me you need speed over anything, then I've found the neatvideo plugin a really efficient way to reduce the noise on animations in octane.
For example, I left a scene rendering for 1 min - took a snapshot at 1080p, and another at 4 minutes. The noise is obviously less on the 4 min image, but it's still very present. However I found that neatvideo can reduce the noise even on the 1 minute image to an extent that it looks smoother than the 4 min render. I find that shallow DOF in octane produces noisy out of focus grain which takes a long time to clean up. Neatvideo can smooth out images really nicely in these situations.
Of course, this is scene dependent, and NR used too aggressively will eventually introduce artifacts and you'll lose detail in the image. I'm not saying this is a perfect solution...But used subtly I have found this to be a real time saver and can seriously hack render times down for those doing long animations. So if you have an image that's 90% there and you don't want to wait another 4 hours for it to be noiseless, try out the demo - it might be useful to you. http://www.neatvideo.com/download.html
It's simple to use but I found that rendering a uniform material with flat lighting first in octane for 1 minute (or however long your renders will roughly be - to give you a sample of the noise type) is the best thing to do. Highlight the noisy area in neatvideo and save this noise profile as a preset. Then use it on the full renders you kick out. I have created different noise profiles for different resolutions. (If you're working in 1080p then make sure you use a noise profile created from a 1080p image and not 720p for example)
If you find that Neatvideo is taking out image detail, you could try rendering even higher resolution so there's more chance it will grab the noise and preserve the details (as long as you create a high resolution noise profile first).
You get even better results using a test animation over a still image. There is a temporal NR setting which works by comparing noise patterns frame to frame, and this can clean images up even further.
I'll upload some images when I'm done with the job, but I'm finding it useful for production renders where I wouldn't normally use octane because of time.