Hussar
Legend
2004? So? Are you saying that's when you started playing?
No Kask, that is not what I'm saying. What I am saying is that if my join date is five years ago, then perhaps, just maybe, I've been gaming for AT LEAST five years. The fact that I started gaming in 1980 is beside the point. I generally find that getting into pissing contests and trying to appeal to authority doesn't help in these discussions. Anyone who is feeling that their points are so inadequate that they require bolstering by telling all and sundry how long they've been gaming should possibly go back and rework their arguments.
Just a thought.
Ok, the 10 things I would want to have completed in two weeks...
NOTE: I am assuming that I have presented a brief summary of Gulmenghast (perhaps a page long) to my players and it is met with approval as a place they want to adventure in...
1. The racial write-ups how they relate to one another, attitudes towards
each other and differences from the generic PHB descriptions... (as an
example in Gulmenghast Shifters, Genasi, and Tieflings are the result of
long-forgotten alchemical and arcane gene-modification of humans with
the essences of beasts, elementals and devils that arose in response to
the invasion of these peoples lands by the Dragonborn Empire thus there
is an ancient enmity between these groups)
2. General descriptions of the 7 wards and The Severed Realms
3. Map of The Pinched Quarter with encounter charts
4. Fleshed out maps of The Quivering Catacombs, Badger Bayham's Brew
and Breakfast, Miss Skifin's General Tradehouse and Emporium, The
Shrouded Bath House, and The Gate Towers (Have no problem stealing
maps off the internet to cut down on work...)
5. General description of the two religious orders in Gulmenghast
6. List of Major NPC's w/stats (mostly re-skinned from MM, again to cut
down work)
7. Macro-level government of city in broad strokes
8. Macro-level political structure of The Pinched Quarter
9. The stats for the Lawbringer's stationed in The Gate Towers
10. 10 secrets; one for each Ward and 3 on a micro-level for The Pinched
Quarter
Now, I have a job, a child and am preparing to get married in September, so I don't have a ton of time... that said I enjoy working on my campaign and I generally devote an hour to an hour and a half before I go to sleep to working on my wiki. So total man hours is somewhere between 7 hours and 20 hours to complete the above... so less than an actual day out of 2 weeks.
Honestly Hussar, I find (and I am assuming here) what you call "adventure" design doesn't take that long unless I choose to do it from scratch without using all the maps, stats, monsters, traps, etc. that are widely available in the books and on the internet. The actual world I'm creating for these adventures to take place in, it's consistency, verisimilitude and logic are things I can't grab pre-made and tweak. I also find that the more fully fleshed out my world is the better informed I am as to the specific tweaks I should make to give it a Gulmenghast feel as opposed to a generic high-fantasy setting 6432577 feel. YMMV and all that of course.
A couple of points here. First one is, please stop with the strawman that if you don't do world building you are forced to have "generic high-fantasy setting 6432577" and I'll stop calling it setting wankery. Deal?

Second, let's not lose sight of the fact that your campaign setting is very small. You're limiting yourself to one city. Not that there's anything wrong with that. It sounds interesting, but, it does cut down on the work load.
But, in any case, let's split the difference on your time estimate and call it 15 hours. 15 hours of work to detail one small setting all before you sit down to do a single adventure. Granted, you've got a couple of locations here to play with, at least you have maps of them, but you have not statted a single encounter, nor created a single adventure. Say that's another 3-5 hours of work for a decent sized adventure.
See, right there, that's my problem with the idea of world building first. You've spent a fair bit of time, and yes, I do think spending 15 hours (give or take) on preparing to start writing adventures is a long time.
And, to boot, you have only the barest bones of setting here anyway. This is just the start. You have several hours of work ahead of you to add any really meaningful detail to most of these sections. Right now, beyond a very small handful of points, would you call this a fully fleshed out setting? I certainly wouldn't.
/disclaimer - the following is a joke, please take it as a joke
What happens when your players want to meet the thieves guild

/end joke.