Water changes should effect the nitrate level as soon as the water is changed. You could do 100% water change and as long as the rock doesnt dry out and the tank is 100% cycled you will not affect the cycle. 25% water change will only drop the nitrate level by like 10ppm. You may not be able to actually see that in the test you are using.
Your nitrates aren’t bad. As many have said read from the top down. What is your goal for the tank? If it’s going to be a mixed reef, soft corals will love the nitrates. If you want to put macro algae in the tank (which is fine) there are varieties that are much prettier than a big ball of chaeto . Lol
That's what I thought. Personally, and this is just me and what I would do, I would give the tank a bit more time to mature before adding anything. I have a 10 gallon that I waited 5 months before I even turned on the light, never mind adding a coral.
