You don't leave one gate and fly light years to another; you use the same
gate for going in and going out. Explorer Ship A comes out of hyperspace;
looks around; decides that there are planets in this area that are worth
possible colonizing, exploitation, that sort of thing; it's a very quick
overview. (Or they go to systems that have been already selected.) They
construct a gate, finish the job, and move on. Other ships can now use this
gate for entering and leaving this system. Is this clearer?

jms