If you are there are opening, make your choice of which to ride first (I would go to Soarin) and ride without a FP, if possible. After riding, make your way over to TT and get a FP for that one....they shouldn't be "out" at that point. And, particularly with TT, if the return time is later in the day, but not at a time you planned to be around, just come back at a later time - example, if your FP return for TT is 3:00, but you have a meal planned or are planning on an afternoon break, just return sometime after 3 that day....they will allow you on no problem (has happened to us many times....we have even used them the next day, if the ride was down at our return time, etc).
If you can't get on Soarin' right away, get a FP, look at the time the next FP will be available (which could be quickly, if the return time isn't too long) and them make your way over to TT to either ride in the single rider line or wait til the next FP time is available to you.
We were there last month and it was busy (not as busy as a holiday of course) and we had no trouble doing both with FP.....but we found at rope drop, we were able to walk right on Soarin...when we got off, the FP return time was only at 10:15 -11:15 or so, which made the next available FP at 10:20....FP for TT would still be have available at that time.
That said, if you arrive mid-day and want to do both with FP, you may have problems.