You can use the liquid immediately, you never "need" to steep, as it should wick, atomize, and all that stuff. It just might taste the best.
Steeping is just giving the flavors a chance to mix thoroughly.
There are methods of speed steeping, using hot water or ultrasonic waves you can learn about, but I don't use so I can not comment on.
My method, let the e-liquid sit around for a week or two before using, keeping it away from heat and direct sunlight. Like keep it in a cabinet and off window sills. There, its steeped.