For this Sunday 9/2/18, is there a warm up band before Pentatonix and about what time might Pentatonix be taking the stage? I have a family member who can't be in the heat long without getting ill.

I don't know specifically, either for PTX. But, when I was there for Counting Crowes w/Special Guest, Live, it was also 6pm (that seems to be HPStadium's regular Sunday start time) & the opener went on just after 6pm. Additionally, you can contact the stadium or box office staff to further assist you (especially in ADA circumstances) with exact info regarding the heat exposure issue. Best of luck & enjoy the show!

From the Lynyrd Skynyrd Farewell concert I attended recently show start time was scheduled for 6pm. 1 st band started probably around 6:30

Sorry can help you out with an answer on that one! I am only into the ice skating club!, but if I had to guess I say no matter what you shouldn't be in the sun to long. The foot traffic moves rather quickly! Hope you have a great time and enjoy the show!