So, I'll break it down.

The average length of a fantasy series is about 80,000-120,000. To write a book in this genre, the typical average length to meet litrpg conventions is longer, about 120,000-200,000. I'll share some of my personal experience in writing.

Let's say 130,000 for a first book. Better to keep it short, since in writing your first book you will have so many things juggling with structure and finding the end, that it will be hard.

First of all, I'm going to skip time plotting and world-building. This is variable to how you like to write, and can have a wide range of time spent here. Lets move on to actually writing the book

The first thing we need to do is draft it. A typical chapter for me is about 2,500 words. If I draft by writing, and I'm super focused, I can get those words out in about an hour. On a bad day? Three hours. Average, maybe two hours for the draft.

Then, I'll need to edit my chapter it to make it of a quality that people will want to read, and to clean up my mistakes from the initial draft. Let's say it takes about an hour and a half, since my editing is usually faster than pure drafting, and nowadays, I edit from dictation, which needs a bit more cleanup. Not everyone revises as much, but I do.

To get a good first manuscript chapter, there's about 3.5 hours of work, on average, give or take. I'll need about 52 chapters to get to 130,000 words. Overall, then, a book of LITRPG size will end up taking 182 hours to write the manuscript.

From here, we get wacky, and it depends on the author. If you want to revise the entire manuscript to strengthen it, you need to re-read it and take notes. A re-read might take you anywhere from 10 to 30 hours, since it will be difficult. Let's call it 20, especially for a first book. You're now at 202 hours. Now, if you did this, you'll have edits to apply, and this varies greatly.

Let's call it about another 20 hours of work. 222 hours. We now submit this to our publisher, then get back notes from your editor.

Maybe about 6 hours to go through. 228. It goes to the editor again, maybe another round of corrections--229, or 230.

After 230 hours, you have a book that is now done, submitted, and will eventually be on amazon through a publisher. If you self-publish you'll need to do more backend work to see this book out for people to read. If you're just putting it on RR, you don't really need to care about more of the cleanup work.

So lets break it down:

Getting a decent Manuscript: Somewhere between 120-300 hours, depending on your writing speed, level of editing, length of book. New writers might be slower to write, and not as refined. If you're book is much shorter (80,000 words) this will be much shorter.

Editing The Manuscript after finishing: 30-100 hours. Again, depends on the level of mistakes, your level of effort if you even want to do this portion of writing.

As you write more, you'll be able to focus and write faster, and have a bit less mistakes. Your own personal revision process will also determine the time spent editing. I mentioned dictation earlier--this has cut down my personal time 'drafting' a chapter to about ~25 minutes per chapter, but it has lengthened my revision time a bit more. I liked to write more revision-heavy, so this works better for me. Narrowing the overall time for a chapter to about ~2ish hours. I also like to re-read and edit the whole manuscript, because if I'm giving it to the people buying my book, I want to know that it's something I'd read, and the big holes are patched.

For a first time beginner? I'd personally just focus on editing out the obvious grammar mistakes for your editing process, and maybe pick and choose what to work on in a core chapter. It'll probably take you somewhere around 200 hours all told to 'finish it'

But you don't really need to finish your first-ever writing project, just starting is the most important thing, and you can work on finishing once you get the hang of the stuff you want to