Different latency in same baud rate

I am trying to get latency of my Xbee modules. I have 2 sets of Xbee and Arduino UNO. So, from one node I am sending some packet in AT mode and on another I am getting the data.

Now the problem is: though I am not changing anything (distance, baud rate etc) the latency is coming different each time. Should not the reading always come same for same data and baud rate?

That would be dependent upon which XBee product you are working with and its associated protocols. It can also be effected by the channel used and the noise in the area at the time the transmission occurred. (IE Retries, Clear channel Assessments Etc).