The pattern instructions for Simplicity 1880 (well, most pattern instructions really) tell you to construct the skirt last. I like to do this first. Why? Well, especially for a skirt that needs to hang, this is a great idea and Simplicity 1880's skirt does need to hang and stretch out before you hem it. I like my skirts or the skirt part of a dress to hang for several days before I hem it. I've always noticed that if I only allow it to hang overnight, I'll hem up the skirt and then it will stretch even more and the finished hem will be all wonky for the rest of the garment's life because I ain't gonna go and unpick it anytime soon. I'm lazy like that.
So I say, stitch up the skirt section first and then either put it on the dress form, or let the thing hang on a hangar until its time to attach it to the bodice. Remember that the double notches go down the center front and center back and that the left side (at least I like my zipper on the left) of the skirt should be left open for your zipper. I'll be leaving the entire left side seam of the skirt open until after I've inserted the zipper as I'm doing an invisible zipper on both dresses. But don't worry if you don't want to mess with invisible zippers. I've got several resources for how to do other types of zipper insertions too.
Once done, you can put the skirt on the dress form or hanger and let it hang. We'll move onto the bodice tomorrow. Yay!