From: Winnipeg, MB
WITP-AE is a much richer game than its predecessor WITP, which was an advancement on UV which I have no experience with.
By "richer", I mean the player has more control over more things but not total control because there are many die rolls and under-the-hood calculations that simulate the randomness of action in war.
If you start with Coral Sea scenario it lasts about a week of game time and can be played out in a day if you are already familiar with the game interface controls. If you are playing for the first time, the scenario is designed to let you try out the controls applicable to carrier and amphib warfare, with a little logistics thrown in. The idea is to try the scenario, then replay it with different setting and replay as the other side to see the differing outcomes from different settings.
After Coral Sea, the Guadalcanal campaign is recommended because it has much more involvement of land-based aircraft and the logistics of trying to support troops on a contested island. That scenario goes from August 1942 to Feb 1943, IIRC, and takes several days to play out.
Much of the time estimation depends on your play style (micromanage or minimal intervention) and whether you can keep at it constantly or intermittently (sometimes you have to spend an hour re-acquainting yourself with what was happening and what your plans were before you took a break for several days).
My personal favourite small scenario is the Marianas one (Philippine Sea). Difficult logistics and Amphib Landings, a huge carrier/LBA battle, ASW, and potential for a huge Surface Combat battle or ten.
No matter how bad a situation is, you can always make it worse. - Chris Hadfield : An Astronaut's Guide To Life On Earth