Light years are a measure of distance, not time. Light has a max speed, it only goes so fast. The further away you travel, the more time it takes and even multiple jumps depending on the strain of your engines. Sometimes you have to come out and let them - well, reboot is the easiest term, like a rest stop on a long road trip. You can't risk the nuclear core going boom on you. Sort of ruins the whole traveling in space thing.