I think it should be okay. If you get to the Character Spot first, you should be out of there pretty quickly (almost certainly less than 15 minutes). You can double check the wait time for Spaceship Earth before you get on and decide then whether to do it before or after Test Track.
Plus, there's a 15 minute grace period built into the end of your FP+, so you've got a little bit of fudge room there, too.
Granted, I haven't been in there with Soarin' closed, but most people are still going to prioritize Test Track and Mission: Space at rope drop, and Spaceship Earth's line moves quickly, since it's a continuous loading dock.
Sometimes they'll let you in 5-10 minutes before the official opening time, too, so try to get to the gate 30-15 minutes before opening.
Have fun!