It's hard to say because not all LR is equal. A porous 3lb selection of LR would probably work better than a more dense 3lbs of LR.
Honestly, the entire discussion surrounding the cycling process is filled with conjecture and only some verifiable fact. The reason I say this is because everyone's tank cycle's at a different speed. Some cycle in days, others cycle in weeks or even months. For instance, I've started with LR and cycled a tank in a week and I've started with dry rock and cycled in about 2 months.
The best thing you can do is ghost feed/dose small amount of ammonia and test everyday to see when ammonia and nitrite are both zero. In a small tank, it probably won't take too terribly long. Just be patient, best of luck!