I would say it depends on what your goal is.
If you want top 5 and launch on a busy day, you'll want to spend a month or more doing prep.
If you just want some traffic to your website, you don't need to prepare more than an hour.
For me, I'm looking for a happy medium between the two. I want to end up on the front page but I'm not looking for any high position.
For something like this, I would say you need a week or more of prep.
At the end of the day, what I think matters more is not time you spent prepping, but the quality of the prep work. You might need more time if you don't have a large audience to build it up before launch, or you might need less if you already have a massive following.
Hope this helps!
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