I recently installed Neat Video for Premiere Pro because I was told it was faster at denoising than AE and it was. The issue is, the day before yesterday I rendered the selected clips that had Neat Video applied and everything looked great afterward, it all played through smoothly in the timeline with noise reduction applied. But when I exported the final video the next day after a few minor additions it still took 5+ hours to render as if it was rendering the effects again...
All my clips with Neat Video applied were still green in the timeline when I exported... I would have thought that the video would export in a matter of minutes as it normally does without having to render denoising. Did I do something wrong or is it a Neat Video bug??
After you've applied Neat or any other noise reduction app and it's processed a clip, any other change you make requires the app to redo the processing.
So ... when you apply video noise reduction, you basically need to do a render/replace operation for that clip. Then the noise reduction process is finished for that clip. It will not need to re-do the analyzation as it's been used to essentially transcode to a new "clean" clip.
You can always "restore un-rendered" back to the original media if for some reason you need to do so. But I rarely need to. And this way, you do this once and it's done.