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I doubt most really have a beef with the time abstraction per se, but rather the consequences it has (and increasingly will have) on history progression and the surrounding world. Right now it's really only a minor nuisance at most but it's bound to get worse and worse as the game develops :>
What kind of problems are going to get worse?
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For example, as have been mentioned all visitors to our future taverns will be forced to stay for close to a season at least, factoring in all the time it'll take to move across the embark, time spent in the tavern, eating/drinking/sleeping at least once etc. This isn't necessarily an issue just from the perspective of fortress mode, but taking the rest of the world in account this could seriously affect the outcome of various events when important historical figures literally are removed from the world scene for a season or more.
Another thing that is already somewhat of an issue is werecreature transformation, and any future features following the same mold of being linked to dates or recurring events. As it is now they only transform for a few moments before turning back, rarely having the time to actually do anything. You could argue that it's simply a matter of increasing the time they are transformed in fortress mode, but with how fast a month passes you'd then end up having werecreature citizens spending most of their time in their transformed state.
The by far biggest hurdle however is when we eventually get to sending out our own armies etc. With how long simply moving around the embark takes, just having your militia gather up and make it off the map could take several seasons. For cases such as being asked to send help to another besieged fortress (which would be an asap kind of deal), this simply wouldn't work without silly fixes such as teleporting them off map as soon as the order is made. Pretty much any interaction with the outside world that from a story perspective needs to be quick would need cheap fixes like that. There's probably ways to solve most of these issues but as Toady have said, it's a lot of extra work to "fudge things". And it might end up making legend mode quite messy for those who like that as its own game mode.
Our fortresses will pretty much always be stuck in a time dilation field, bending things out of shape every time we need to interact with the outside.