Your datasheet page 17 show "Take SYNC low for a minimum of 4 MCLK cycles, if
required, to synchronize multiple parts."
As for the AD7762 internal working,
after get the /SYNC L to H edge, your ADC start to work, correct?
If so, what is the time from "/SYNC L to H edge" to start to work internal circuit?
I cannot catch this on your Fig-2,3 timing diagram well.