We love TT, but it definitely can be tricky. It seems to go down for random things, plus it doesn't run in the rain. And some times of year it rains. A lot.
Your plan will likely work just fine, but I would suggest making a change and pre-booking your tier one for Test Track and look for Soarin' as a 4th.
If you have a FP for Test Track when it goes down, you can use your TT FP any time that day if it comes back up. If you have a FP for Soarin' and Test Track goes down, it'll be harder to get a 4th for TT. It's just better insurance that you will get to ride TT.
Plus, Soarin' is easier to get as a 4th FP, and it often has reasonable waits in the evening. In fact, last June I went there around 7:40 pm with my 4th FP, and there literally was no standby line. The point where standby people and FP people were being merged was where the "line" started.