You can see time flight in the pix4d Capture, after you deffine your mission size and mission settings. For P4P between 16-23 minutes per flight.
For multiple misson battery change:
https://community.pix4d.com/t/6407–Android-Battery-change-on-Pix4D-running-on-DJI-CrystalSky
On iOS there is also an option for multiple mission battery change, but its not working currently (it resumes flight but it doesn’t take pictures)