If you are finished with your goal # of observation hours, your references are ready and of good quality, you have pre-reqs almost or fully completed, and you don't plan to retake your GRE then you are ready to submit. If you can improve any part of your app before the program deadline, then wait until you have done that. (I think you can still add verified observation hours after submitting though, but double check.) The earlier the better for rolling admission schools!