21 days.
Upgrades cost the same at any level so sometimes it's better to save money and buy the higher level later.
Ex: Max Rocket fuel is 10k regardless whether or not you bought lvl 9 rocket fuel.
Dismantle your useless turret.
Use that money to get 3 stars of supply line.
Build a destroyer/bomber to deal with any beginning crap AI sends at you. Max supply line. Get a few stars of recycling and a few in factory.
Save up until u have 2000-3000 credits.
mass destroyers. Win