Counter source used within DAQ Assistant CO pulse time

Hello, I learning to use Counter Continuous Pulse Output on USB-6363 OEM.  I used DAQmx Create Virtual Channel (VI)  CO pulse time.

Though OK, I need to know what is the source (or time base) the counter is used to generate the Pulse train.

My goal is to create 3 synchronized continuous pulse outputs (ctn0,1,2) with defined delays and duty cycles for each.

Thanks!