'Shark Tank' investor Robert Herjavec reveals how deals are affected by what happens behind the scenes

"Shark Tank"/ABC

"Shark Tank" investor Robert Herjavec.

When "Shark Tank" returns on Sept. 23 for its Season 8 premiere, millions of Americans will tune in to watch a reality show with real stakes, where entrepreneurs pitch their companies to a panel of investors who can potentially change their lives.

A great product and charisma are necessary for a deal, but a bit of luck is involved as well, since the Sharks' moods are closely tied to their shooting schedule, cast member Robert Herjavec reveals in his latest book, "You Don't Have to be a Shark."

The series has been huge for the personal brands of each of the six investors and has yielded investments that have made them millions of dollars, but they need to spend as little time as possible in the Los Angeles studio because their businesses are still their primary responsibilities.

To compromise, the show's producers have worked out a schedule that allows an entire season of about 30 episodes to be shot over 17 days. The seventh season, for example, was split into a session early last summer and then early last fall. Each day on set lasts 12 hours, beginning at 6 a.m. or 7 a.m., and shooting is done in three-day splits separated by an off-day.

In his book, Herjavec says that each of these three days has a distinct atmosphere, and the day an entrepreneur pitches to them on affects their chances of getting a deal - as well as how the Sharks interact with each other.