Just installed my spoiler using 3M...it's been a few hours and I can feel it becoming more and more solid. No gaps, even up close - I'm satisfied. If anyone's curious about the tape's cure time, I found this on 3M's FAQ site:
Immediately after an application is made, about 60% of the bond strength is achieved. As the adhesive continues to wet-out the surface, you can expect the bond to be at about 75% - 80% after 24 hours. After 72 hours, 95%+ of the bond strength is achieved. The bond will continue to build with time.