Dual Viair 480c issues

I have dual viair 480c compressors to fill a 12 gal tank. it seems like it is taking way too long to get pressure up. I have the compressors wired like the dual compressor set up wiring diagram using 6 ga wire from the battery to a distribution block and the 8ga wire going to 2 30 12v relays, (1 for each compressor) and 8ga wire for the grounds.

What is the time required to go from 0 psi to full pressure and what is the full pressure?

The wire gauge versus distance versus current table on page 6 of 8 of the User Manual should be followed.

I talked to a guy at viair. He said to check my check valves.