Well, my best is now 7. I can feasably see it taking 4, but you would need an awful lot of luck on the first couple of launches. Im gonna keep trying for it though
Been trying a while and had four days once of twice. I just got three days: managed to get a few yellow launchers on first day and upgraded band and launcher height (~$50 x ~600ft x ~40 seconds). second day got lucky with height and yellow/green launchers (~$45 x ~1200ft * 40sec). Upgraded band all the way, launcher almost all the way, and added three E-Rockets. Blasted all the way out of space with the E-Rockets on the third day.
I see it feasible (although highly improbable) to do it in two days, but that what I'm trying for now...