I know "certain people" who "start" around 9 p.m. the night before their "day hike" date just to make it to the summit at sunrise.
I used to "rush" to the summit. Now, I "rush" so I can get back to the Portal Store for "Froth and Fries."
You may want to hike San Gorgonio and San Bernardino. Both require permits and Adventure Pass. www.sgwa.org.
You may want to look at hiking Humphrey's Peak in Arizona before you July Jaunt. Just an idea since it is near the Grand Canyon.
Being in shape is half the battle. You need to log in the mileage at altitude.
Since you are in SD, you can "toughen" up your feet by walking on the dry sand with your pack weighed down with sand and walk barefoot. Trust me, it is a great workout! Forget the tubers with their surfboard stares. Yeah, they can "hang ten" but can they "hike 10k+?"
A lot of great ideas have been posted.
Best of everything to you on your big day.