Hello,
Yes, you can apply through optomcas in July without your OAT scores bc NOVA will get them since you will have to request on your OAT application form for NOVA to receive your scores. You will get 5 scores sent to schools included with the OAT app and $25 additional for each extra school. It takes the school a few weeks to receive your score, but you can always fax your unofficial score prometric will give you after your test. Nova might look at your app before OAT, but they will not make a final decision until your scores come in. The best advice I can give you is, don't take the test until you feel confident you will do well. If you plan on taking the test in August, there's no big factor if you need to post-pone it a few weeks. In the end the decision is up to you. Good luck with the application cycle.
