The sample time of the signal depends on the rate at which the signal was acquired. You should refer the source from where you got the data to figure out what sampling rate was used to get it. It depends on the hardware and the acquisition method used to store that data.
To answer your second question, "find delay" block finds the delay between a signal and a delayed and possibly distorted version of itself. You cannot randomly come up with a Reference signal as it would not make sense to compare two signals which have no co-relation.
Refer the following documentation to understand more about the functionality of this block:
