Trying to figure out how long it should take iRay to render a short, 3 second, video.  Here is my system

How long is a rope, how much does a car cost? There's no quick answer to your question as it depends on the complexity of the scene, including lighting, materials, animations. A 1070 GTX isn't really the most powerful GPU for Iray. Even my 1080 Ti isn't really much use for anything serious other than stills.

Gerry

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System: Win 10 Pro (21H2), Asus X99-E WS, CPU i7-5930K -3,5 GHz, 32 GB DDR4 2666-16 RAM, NVidia GTX 1080 Ti GPU - 11 GB VRAM(Driver Studio-536.99), Samsung 850 Pro 512 GB SSD, 6 TB HD storage.

I did some tests a while ago and with optimization it came to around 1 minute/frame with a GTX 1080 Ti.

Optimized means that I rendered out at 1280x720 and used 200 cycles with denoising turned on for the last 2 cycles. I then used Giga Pixel to upscale to 1920x1080.

So for 3 seconds at 30 frames/second (90 frames) you would need 90 minutes (1.5 hours) with that setup. 

But like Gerry said, it depends on many factors. The simplest way to get an idea is to time the rendering of one frame of the intended scene and then multiply accordingly.

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@Animagic
Speaking of Giga Pixel AI. I recently bought Video Enhance AI (mostly to restore old videos).
Before I had to split videos into frames and process them via Gigapixel and then assemble back.
It was slow, and inefficient process.And the result is not always satisfactory.
With Video Enhance AI it is much faster and it is specifically optimized for processing videos.
I only tried it once with Iray scaling 720p to 1440p. Came out fairly well on architectural render: https://youtu.be/noLxKen0Y4M (second part of the video)
Yet to try rendering hair and such.