Get the boarding pass the day before my flight at the checkin counter
I will flying out of a regional airport in a few weeks, the itinerary is XXX-EWR-NRT and a separated ticket NRT-GUM, all on UA. I am not eligible to enter Japan, so it's impossible for me to check in online and get boarding pass. I am little bit nervous that the checkin agent may give me hard time to checkin, since my XXX-EWR flight is very early in the morning, I don't want to risk argue with UA agent and miss my flight, is it possible I can visit the checkin counter the day before (and within 24 hours) and get my boarding passes? Any similar experience?
Thanks in advance.