Rushing

From Starport: Galactic Empires

While building a planet you have two options, you can set your planet to building and it will build the buildings automatically (assuming the correct amount of resources are on hand) or you can "rush" the construction for a price. You still need to have the same amount of resources but you don't have to wait for the colony to build itself. The cost for rushing is directly proportional to the amount of time left on the building project. More time = more money.