iPad 4 wifi taking 36 hours to download ios8.1.3?

I have an IPad 4 32gb wifi. It performs pretty well but I got a new laptop and decided now as the time to update my ipad to iOS 8.1.3 since I couldn't before due to lack of space.

I have the newest version of iTunes. I started to download the iPad iOS 8.1.3 update and if said 46 hours on the laptop.

I decided to make some space on the iPad to download the update that way instead, without the laptop.

This way it says 36 hours and won't go down. This is just downloading! Not updating 😟

I have turned the iPad off and on again (best way to solve a problem, surely? 😝) and that reduced the download time to 23 minutes, then it sprung up to 36 hours again.

I really don't know what to do.

I haven't updated my iPad in a long time - its currently at iOS 7.0.4, which means I'm trying to go from 7.0.4 to 8.1.3

Is this the problem or is there something else? My wifi isn't particularly slow, it runs everything else at a fantastic speed, yet even when I try this download as the only thing happening in the house, still this huge wait.

Can someone help?