how much labor time to replace the BCM

There are a few things at play here. Does the BCM come programmed from Nissan, where is it located and does the person/shop have the correct equipment and information to do the job correctly. A shop will usually look up the first two and be able to price it once they have taken a look at the vehicle. A shop/individual should not attempt the job if they don't have the third part of the equation.