I am working with time critical systems where latency of the WSN is greatly important for controlling
You're working with time critical systems and wanna introduce twice the latency by using two XBee transfers on your route from the sensor to the controlling PC? And if your timestamping on the Arduino, what's with the latency introduced by the XBee transfer from the sensor to the Arduino?
How critical are your systems? Is it in the seconds, the milliseconds or the microseconds?