I don't think it would be harmful to wait till tomorrow. You already did one today, and I wouldn't want to stress your fish too much by doing another one right away. Although your fish would probably be fine either way so it's really up to you, but it's already 10:30pm where I'm at so I'm inclined to say wait until tomorrow. I believe that the typical high nitrate zone for a FOWLR is 20ppm and your below that. I also agree with Khij, if you can wait and do a larger water change, that would be better.