I definitely think that days should be made longer, and that all of the actual tasks should be made to take a lot longer. Mining should be a big undertaking that takes time, especially longer time for harder rocks and such. Digging out a giant city underground shouldn't be something you can easily do with just a single dwarf over a short period of time. It should be more like having to carve out something small at first, and slowly expand later with a team of dwarves working. As well as crafting taking a much longer time, rather than turning out suits of armor like a factory. Making walking speeds a bit faster if possible would help out as well. And of course anything that allowed for increased speed, path caching, multiple processor support, etc. would help.
Much longer days could also be very nice once a few more features get in. Allow for an actual day/night cycle, lighting effects making it darker at night, perhaps even dawn/dusk, etc. even temperature differences, water freezing over at night in colder areas when it gets closer to winter. A scorching desert where workers have to go out at night because the day is too hot to work or go outside, etc. Having schedules for day and night times.
The years might end up quite a lot longer, but they could always be shortened, if necessary, make each season a month long or such. In other words, pick a good length for a day, pick a good length for a year or a season, and make the number of days/season to match.