Took me an hour - I have BT's fibre-thingy so it's pretty fast.
One thing to note that narked me off quite a bit is that the system default power off setting doesn't seem to regard game downloads as activity and will shut your Wii U off midstream. I had gone out with my daughter after purchasing Nintendo Land which estimated a 40min. download time and clicked the "power off when done downloading" button.
I naturally assumed when I came home and found the machine off that it would have completed, fired it up to see no new game channel and when I chose the download manager (why it is it I can only access this by clicking the Home button on the Gamepad?) see that it was resuming a download only %55 complete! You'd think it would have let me know that clicking the button earlier would have no effect due to the current power management settings or (more intelligently) that the system wouldn't shut itself off in the middle of any downloads - not just system updates!
Needless to say I've disabled auto-power off completely to avoid a repeat incident. I guess it's to be expected with a system launch to have a few issues, but honestly if you're selling retail downloads I'd expect a little more sense!
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