When should I apply if I am planning on launching a mobile app for iOS in August?

You are correct to apply for both patent and trademark sooner rather than later.

Your understanding is correct. Under the America Invents Act (AIA) we now have a first to file patent system. So, you must file your patent application (provisional or otherwise) before others, if you want to own the invention. Accordingly, anyone in the business of developing patentable subject matter should "file early and often" if they intend to protect their inventions. The provisional filings can be rolled up into a nonprovisional (utility) or international (PCT) application within a year of filing. Under U.S. trademark law, you can file an intent-to-use (ITU) trademark application to preserve your trademark rights against subsequent users. The advantages of the ITU application are that you only need a bona fide intent to use the mark in commerce to apply, and it gives you an early constructive date of first use as of your application filing date. You should also consider filing one or more copyright applications for your mobile app and its unique and creative user interface and software code. As always, you should consult an experienced intellectual property attorney to fully explore your particular facts and options in protecting your intellectual property.

It is safest to file your applications before you launch. You risk losing rights and more if you don't.

For the patent application - apply before you launch. For the trademark application - file after you have launched.