Fortress mode and adventure mode work on two very different timescales, which as Toady has discussed in the Talks, creates some weird anomalies.
The time scale in adventure mode is pretty normal and not particularly problematic.
In Fortress mode, things happen on two time scales
simultaneously, which is why it is problematic.
See this article to understand how time works:
http://df.magmawiki.com/index.php/TimeCertain things are sped up:
The passage of time: It's 72 times faster than the timescale of adventure mode. This is so that the calendar doesn't pass at an unreasonably slow pace for the player.
The completion of most jobs: They seem to be completed relative to the passage of time, for the most part.
Other things happen in "realtime", or rather, on the same apparent time-scale as Adventure mode:
Movement of creatures
Physics (falling stuff, the flow of liquids)
Combat
Hauling
Mechanical triggers
This causes Toady One and Threetoe some difficult design decisions, because time is so anomalous and inconsistent in Fortress mode.
So, what if "Fortress Time" is separated into two different speeds?
In addition to pausing and stepwise time progression (with the period key), you'd have a "realtime" mode and a "fast" mode, and the ability to switch easily between them.
In realtime mode, time passes as it does in Adventure mode. The things I listed under "realtime" above would be unchanged in this mode. It would also take a long time for seasons to change, and tasks that realistically would require a lot of time to complete would occupy your dwarves for a longer period of time. (Mining, making things, etc.)
In fast mode, the things listed under "sped up" above would be unchanged. Time passes quickly, seasons change at the speed you're used to.
The difference from current "fortress-time" is that movement and physics must be sped up. Dwarves zip all over the place rapidly. This is the problematic part of this suggestion - it would require a reliable method to simulate something that is already processor-intensive happening much faster. I'm not sure this is even possible for fluid physics.
But I could be wrong, so I'll continue to explore the idea:
Hauling tasks would be less of a drain on the fortress, since they would be completed much faster relative to other jobs. In designing a fortress, you would not have to worry as much about distances.
Eating and drinking would take up less time, and also be less of a drain on the fortress. This means dwarves can eat and drink more frequently, and consume food at a more realistic rate.
As well, characters would be able to have a more realistic sleep pattern.
Something which should be addressed regardless of whether this suggestion is considered is that the relative length of time that certain tasks take to complete should be more carefully considered regardless of skill. For example, carving a large pot out of stone should probably take a lot longer than making one out of clay and firing it in a kiln. Some tasks may even take several days to complete--in which case, it should be possible for it to be completed gradually in multiple sessions. I can already see some of this in jobs such as mining, where a wall can be partly mined, with a faded appearance, and finished later.
In response to certain events, such as ambushes or combat, the game should be forced into realtime mode until combat is resolved, so that hostile encounters won't spiral rapidly out of the player's control.
This also has implications for adventure mode. If the duration of jobs is made more realistic, then it would be rather awkward to make such actions a single-turn event. Perhaps, when performing a long-duration job in adventure mode, it would actually switch to realtime or fast mode until the job is complete.
So basically, using a gameplay mechanic with precedence in many other games, all of the temporal anomalies resulting from the weird timescale of fortress mode can be solved completely, and the only hindrance to this solution (from what I can tell) is coming up with a way to rapidly simulate or generalise creature movement and fluid physics.