Honestly, you should plan to arrive and drop off your luggage by 9:45 if you have a 10AM check in time. Most likely they will make you park in the outdoor lot. By the time you park and walk over to the terminal, it will be 10. I couldn't 100% vouch for arriving 9:15. All I can say is, I've not only left from Cape Liberty, but I've driven friends numerous times to the port. By 10:15/10;30 it seems that it gets super congested leading into the port.
Watch the 1st 45 seconds of this video to give you an example of what I'm talking about. I know it is from 2019, but things have not changed much. The video vlogger claimed this was at 11AM.