To go through the quest line to get the whole farm open, a couple of days. You need to be revered I think in order to buy the seeds for the herbs. But trust me, it's worth it. I always get at least 1 per 8 i plant every day. The seeds take 1 day to grow. Also, fly around the daily area in Valley of the Four Winds (up on the mountain to the west). You get a shit ton of green tea leaf, but you find the occasional golden lotus by itself, and the tea leaves also drop lotus as well. I've gotten most of my lotus from the farm though. Get a farm built for all your 90s and you will bank in the lotus.