[AD9371] Rx/Tx/Obs Rx PLL locking time


I have a question about  the PLL locking time of AD9371.  It is about 200ms according to the user guide document, and also about 1000ms accodring to the reference code. 

why does it take so long time to lock the freq?  Can we decrease it  to  hundreds of us? if not , what  is the reason?

Thank you!
Best regards.