We're running through the War of the Burning Sky. We play once a month, for 4-5 hours tops. Usually around 3.5.
Our regular GM is out of town for a couple of months, so I took over for the Trial of Echoed Souls module.
If I ran AS IS, I estimate that it would take our group at least a year, and possible closer to 18 months, depending on which paths were taken and what people wanted to do. Given our pace, it was my duty to cut it down to, at most, 6 months. That means no more than two months for each of the three acts in the module.
I sat down with Primitive Screwhead (our regular GM) and went over the module. We streamlined the first act down to four total encounters, or two per session. Where other things were planned or necessary, it became necessary to roll those 'information bits' off into other encounters or gloss them over. There tends to be more "railroading", but only in the sense that we don't have the time for people to spend 3-4 hours running down red herrings before getting back on the path.
Some things just get completely glossed over - such as the whole flavor of the forest. My joke was that, in a D&D world, the "unnatural" elements of the forest are completely natural. So much so that I nicknamed it "Generic Evil Forest 3-B", then used that as a basis to set expectations of what they would find and encounter so that we didn't need to bother with endless minor encounters and flavor blocks. Now, some groups or people might be bothered by that, but not our group. It meant that they know "evil **** happens here, don't be surprised" and we take it for given that the characters deal with it appropriately.
Hey, more time, more flavor. Less time, more handwaving.
Experience point wise, I haven't found it to be an issue. We don't track XPs normally. We just level up every couple of months as needed.