XBee Pro S2C - Read NJ timer

Hi All
I am using the NJ parameter to allow joining to my network for a pre-determined time. What I want to to however is monitor the XBee module and read back something that tells me if the module is still allowing joins (ie the timer has not run out). I know I could send the NJ command and then start my own timer, but this does not seem to be the best way. Is there a command I can send to tell read if module is still allowing joins?

Many thanks