I should also add that it was quite slow and laggy ( Single digit fps ) during history/legends/erosion cycles. It actually froze a few times. I suspect it wasn't liking the no rejections.
You get a low framerate during most of world generation. It doesn't update until it finishes some large scale task (e.g. a battle) because it doesn't need to update.
As far as the delays, my current world took easily 30 minutes, probably 45, to run history. Everything else was fast (it was a painted 129x257 world -- all hail Excel and Notepad for assistance in tedious pattern generation and pure-text formatting, respectively), but history frequently froze. Every 5-40 years something huge must've happened (I've yet to browse the history in detail), because it'd freeze, sometimes for upwards of 30 seconds. It probably doesn't help that there were enormous livable territories and three times as many civs as in unmodded DF.
When the history generation freezes, it can seem like the game locked up entirely. Just give it time and it'll probably fix itself.
If it locks up entirely during the initialization phase (before it starts counting from year 1 up, but after erosion), you may have a raw problem. Alternately, you may have too many caves. In previous (randomly generated) worlds, I've had to reduce the cave count (not cave size) to avoid apparent lock-ups. It may not have actually locked up, but the pause certainly outlasted my patience.