Have you been watering it 3x per day (morning noon and night)? Water for about 10 minutes, 3x per day for the first few weeks of putting it down. Then after the roots are connected, start to back off on watering until you are watering deeply but only once a week. How long and how frequently depends on your soil, soil structure, grass type, grass mowing height, sun/shade, humidity, temperature, and wind. It also depends on your sprinkler's ability to apply water. My sprinkler only delivers 1/8 inch per hour over 900 square feet. I water once a week for 3-5 hours during the hottest part of summer. I have St Augustine grass mowed down to 4 inches on limestone soil under the full shade of tall oak trees.

I rarely see someone with much experience with zoysia here. Mostly when we do, it is someone who bought the sod from the back of the magazine, got disenchanted with it, and switched to the most popular grass in their neighborhood. That's not very good experience to learn from. We need some people from Japan and the Philippines to help out.