One of the most important jobs we have as writers is to make sure that we grab the readers interest right from the get go. The second, of course, being that we keep that interest throughout. But without that initial hook, the latter becomes redundant.

So how quickly do you need to get that hook in?
Some schools of thought say it should be the very first sentence. That’s when you need to grab the reader. Personally I’m not a big fan of this method. Yes, your opening line is important, but should you rely on that one sentence to carry the burden of everything that follows? In my opinion it’s too much pressure. It also increases the chances of the dreaded purple prose.
It was a dark and stormy night.
Paul Clifford by Edward Bulwer-Lytton
We all know that one. It is probably one of the most derided openings in the history of literature.
My own preference is that the first page should be the hook. Maybe even that entire first chapter or the prologue if that is how the story is structured. But that first page will allow you to set the feel of the prose. You can go into more detail and give your audience a richer insight. What we want them to do is to want to look beyond that opening. To turn the page and become invested. You can have the greatest opening line ever penned but if the rest of that page doesn’t match up to that standard, they will lose their interest very quickly. A narrative is a marathon, not a sprint. Remember, no one turns the page after the first sentence.
You have the space to build your opening. Use it wisely.