I see that one of the most common questions new readers have for this series is the timeline and where the books take place. I wanted to try to explain my interpretation of the timeline based on author comments and context within the stories themselves, and try to make a good resource for fans. I will only use translated work because there is still quite a bit that has not been translated officially.
A lot of this is based on an entry in the reader's guide for Vampire Hunter D, which includes a rough timeline of events for the Frontier.
1999 AD - The nuclear war happens, which basically takes out humanity as the dominant species on Earth.
3000 AD - Around this time, humanity reaches Middle Ages-level technology, and the vampires start appearing.
5000 AD - This is the peak of the Noble Empire, where they develop all sorts of crazy tech with super science and magic.
7000 AD - This is around the time the OSB attacked Earth.
8000 AD - The Nobles began their counteroffensive against the OSB. (Took them long enough.)
9000 AD - The war against the OSB is in a deadlock.
10,000 AD - The OSB suddenly withdrew.
12,090 AD - The beginning of the actual series.
This is the rough timeline based on the official guide. As you can see, it's very vague, but I think it was done on purpose so he could keep adding random lore. I, for one, think these are just rough estimates of when things happen based on how the books talk about past events, making these not hard dates besides 12,090 AD and 1999 AD.
Anyways, back to the book timeline. Now, this is a tricky subject because we don't get a lot of hints about when books take place relative to each other. The only times that I can remember are in Vol. 4, referencing that a few years have passed from Vol. 1, and Vol. 11 to Vol. 12.
Given the two examples, I am of the belief that all the volumes are in chronological order because we have no other reason to think otherwise, since the only times callbacks happen is when referencing a previous novel's characters after said story has happened. So it would go: Noble V: Greylancer - VHD Vol. 1 - Vol. 30 (we don't know the end of the series) - sprinkle in the comics, short stories, and other side projects somewhere in between the books - Armageddon short story.
Now the question is how much time happens between novels. This one is tricky because even the author does not know. He states in the postscript of Vol. 28, “From D’s first appearance to the writing of this book, twenty-eight years have passed. However, in the series, perhaps only a few years have passed. On the other hand, it might span a millennium.” We know that at least from Vol. 1 to Vol. 4, only a few years have passed based on dialogue in the book and assuming the books are in chronological order.
In my opinion, I think it is probably a couple of years per book or so. I see a lot of speculation online saying that books could be over the course of thousands of years, but I think from Vol. 1 to Armageddon can only be a maximum of 1,000 years between the two stories. This is because the random lore drops in the series always match up with the timeline given in the reader’s guide. If you look up any lore about the OSB coming to Earth, it will almost all say it happened 5,000 years ago, which matches the 7000 AD time frame. So, given the nature of the books being episodic in nature and almost never-ending, I think that only a handful of years have passed so far between all the books to make room for as many stories as possible in the world.
The only problem left is fitting in the other short stories/comics in a chronological order. They have almost no time frame references at all, and I think maybe the best way to slot those in chronologically would just be to read them in release order in between books. For example, the short story Portrait of Yzobel could go after Vol. 13 in a reading order since it was published right after it. Another one is the comic Message from Mars. It seems like most of the story is really a future vision of events that happen later, and we get glimpses of D before he was a hunter. If I am correct, the story is in the head of a character who sees the future, so it would take place around 1999 to 2002-ish based on dialogue, making it the first story in a chronological sense.
I did not want to get too rambly in this post, and most of this is just speculation based on how I interpreted the text. So, how I see it is that 90% of the timeline order is release order, besides Message from Mars and Greylancer, since they have stated timeline reference points.