As others have said, calendar time to build a section depends on how much time you have to build on a daily/weekly basis, experience level, whether you prime internal parts, overall attention to detail, amount of rework (I rebuilt an elevator for example - first one was probably fine, but I wanted better). You should be able to get a sense of your style and time to build after the first couple of sections, but sections aren't the same in terms of time. VS takes very little time, HS and elevators are more involved: sections with trailing edges (rudder, HS) and rolled edges (rudder, elevators) take some extra time that may include bonding trailing edges and forming leading rolled edges. Look at plans and take into consideration the number of parts and associated prep time etc.
Another factor to consider is not only wait time for the kit, but your distance from Van's and shipping method - if you're using Partain you may want to consider their schedule. Also - if you have room to store wing kit while still building the tail it might make sense to order sooner to avoid any risk of interruption (wish I had done this with fuselage which I did after tail).