Hi Ian!
The sampling instance for the ADS8363 is not actually dependent on t1 from the standpoint of the CLOCK input. The t1 setup time is related to the point at which the conversion actually begins - the entry is there in order to help define the timing parameters needed to achieve full speed operation of the ADS8361 device. If you happen to miss the t1 setup time, the conversion will start with the next rising CLOCK edge, but the sample and hold switch opens regardless of the CLOCK state, indicated by BUSY going high.