Just returned from our 10 day trip last night.......<<<sigh>>>.......
My recommendation - get your Fastpass for Soarin' as soon as you get to Epcot. On our first visit to Epcot (this trip) we snagged a FP as soon as the park opened. Actually, my kids and I high-tailed it to Test Track while my husband hoofed it to Soarin' to get a FP. He said there were hoardes of people in lines to get their FP's. Our return time was 10:30 - remember this was at opening of Epcot.
We got another FP the same day around 11:00 (or whenever we returned to ride) and the return time was 4:30. With our FP we waited in line 12 minutes before standing in the staging/preshow area.
Our second visit to Epcot (this past Monday) we arrived later in the day - 2pm and got a FP for Soarin' right away. The return time was 8pm.
It is definitely the most popular attraction at Epcot. Hands down. We were able to walk on to Mission several times. Soarin' definitely requires strategic planning.
Have a great time!