Basically, how long does it take for electricity to determine there is a closed circuit and how does it know that the circuit exists?

I'm curious to know how it knows there is a closed circuit at any length!

Edit:

For clarification of the thought experiment, picture an electrical source of some type with a 1 light year wire coming from both terminals and connected in the middle. The wires are of zero resistance and capacitance.

If electrons were to start flowing immediately then information (one end of the circuit knowing the ciruit is now closed at the opposite end) has obviously travelled FTL which is impossible.