There are two types of costs: Building upkeep and production.
Building upkeep is obvious and does not need further explanation.
There are three production categories: Military production, social production and research. A planet has a certain production capability and which percentage of this capability gets filled depends on how the sliders on the economy screen are set up and also to your planet's production focus.
The important thing is that unused production capability does not cost you anything. So if you are not building anything on your planet, the social and military production capability on that planet is wasted.
Note that if you are not building and social improvements, unspent social production goes to military production if you are currently building a ship. But the other way around does not hold.
The income displayed in the civ manager is per-turn, the actual length of the production queues has nothing to do with it, only if there's anything building or not.