Absolutely a priority lane for J class (and OW elites) and in my experience having done this well over a dozen times, 10-15 minutes is what the process will take. The set-up is not great, as there is limited space to repack after the check, but it moves along fairly quickly. Leaving the lounge at the T minus 60 minute mark should be totally fine.

And, yes, if you are in the queue prior to the boarding cut off time, you'll get on the plane. More trouble for them to offload you than to move you through.