NI-DAQmx uses the AI Convert Clock timebase to produce the delay.

If you set this property to DAQmx_Val_Ticks and N is the value of Delay, N pulses of the AI Convert Clock Timebase occur after receiving a Sample Clock pulse before the acquisition of the sample begins.

If you set this property to DAQmx_Val_Seconds, that number of seconds elapses after receiving a Sample Clock pulse before the acquisition of the sample begins.