Two-a-Day racquetball conditioning

I am very fortunate to live between the two physically closest LA Fitness locations in the world (per local rumor). (Akers Mill and Marietta South) In preparation for the 2014 ACA Fall Classic Shootout at the end of September, I am stepping up my local competition. I play at the Marietta South location Monday thru Thursday evenings from 6 – 8 pm. For the rest of September, I will also be joining the Akers Mill crew from 6 – 8 am on Tuesday and Thursday to get that extra bit of variety from my opponents and endurance from myself. In the past, I’ve also played with the Towne Lake crew on a Friday morning about those same hours, but the drive into work from that location just takes too long. Thanks to this plan, I did play against three new opponents for my USA Racquetball donation challenge, bringing me up to twelve distinct opponents in September so far.

Theories on whether or not two-a-day workouts are effective/safe/productive/etc.:

Safe to Work Out Twice
The Advantages of Two-a-Days
Why twice a day workouts work
Are two-a-days ever a good idea?
Two-A-Day Workouts: Helping or Hurting Your Fitness?