From Dwarf Fortress Talk #4:
...Now right now the world is not so big that you can't walk across it in ... what does it take in adventure mode, I think you can step twelve tiles in day? I really don't remember. So if you're in adventure and you can go twelve tiles in a day then even in a large world you can go twenty or twenty two days to cross the entire world. So if you take the caravans time and up it up - up it up, up it up, that's great - if you shoot it up by like five times then it would still take a hundred days to cross the entire world, and if that's the case then there shouldn't be problems with not getting a dwarven caravan every year, even if they stop at various cities, even if they stop a city for like five days and move on...
The time taken to travel from one side of a large world to another isn't too bad. 22 days sounds right. Given traveling a local tile in adventure mode takes 11 seconds, that would mean it would take about 25 days to travel from one side of the map to another on a large map. Assuming you can move at an average of ~3.3 mph (avg. human walking speed) the entire time (no stopping for anything), that would make the map about 1990 miles by 1990 miles, which is a reasonable size.
So, perhaps changing adventure mode time (or at least adventure mode walking speeds) should be a no-go.
So I have a suggestion that builds off of what others have suggested.
Speeding up movement speeds of entities in fortress mode might do the trick given the following are addressed:
1. Combat speed
2. Time taken to eat/sleep/drink/take breaks
3. Possible CPU issues (which might be impossible to take care of...)
I could be missing some very important issues... so my suggestion might be full of shit from the get go. And if issue #3 cannot be taken care of, then this suggestion is totally pointless.
But, let's assume speeding up movement speeds doesn't require ungodly CPU abilities.
For issue #1, simply increase the speed of things in combat so that they match adventure mode time...
For issue #2, things get tricky. A lot of these things have already been mentioned... Breaks could be left alone, but eating and sleep would have to be modified... I don't like the idea of making combat units a special-case thing where they magically have different eating and sleeping requirements by virtue of their military designation. This would be open to exploit...
We could keep eating/sleeping/breaks time requirements the same, but the major thing that this would eff up would be prolonged sieges. If your dorfs take a month to sleep or something, and in the middle of a siege your military dwarf goes to sleep and then a 2-day-long prolonged assault happens in adventure mode time, then your dwarf is asleep for the entire damned time. I could sort of live with it, but I know a lot of people wouldn't be able to, and I wouldn't be entirely satisfied. I mean, I could totally see this not being as big an issue as people think, and I could explain at length what I mean at a later time... But I'll suggest something else for now...
What would be most satisfying to me would be to shrink the time difference gap as much as possible and live with the fact that maybe dwarfs might be eating several hour long meals and sleeping longer than 8 hour (in adventure time) increments. To do so, first make fortress time a bit slower, as in have what would now be one year of game time be like one season of game time. Job time requirements could be increased to compensate.
Focusing on eating, perhaps things could be done as suggested before: Effectively increase the yearly eating requirements by a factor of 4 or something (so, instead of eating as they do X many times a year, they eat 4X or more times a year). Increase food yields per year to compensate. Decrease the time it takes to eat by whatever factor. Keep in mind also, the increase in travel speeds would make eating a bit less time consuming...
A similar thing could be done for sleeping.
Ultimately what my suggestion would make fortress mode end up looking like, I think, would be largely the same, except instead of dwarfs being easily seen traveling from one point to another, the dwarfs would be jumping around. They would still be going through places, it just wouldn't be visible. I wouldn't mind that, myself. Things would appear as normal if time was slowed to adventure mode time. Basically, everything would be operating at the same time more or less between modes, with the exception of eating/sleeping/taking breaks.
Perhaps I'm missing some very important issues. But I think this combination of ideas could work! Whatcha think?