I'll be arriving from the west coast on EWR on United around 9AM and departing EWR on CO at 6:30PM. Assuming UA will not interline my luggage with such a long layover (they probably will, but I'm looking at all scenarios here), will CO allow me to check my luggage that early so I can have lunch in Manhattan?

I've had UA deny me checking luggage outside of the 4 hour window. It's an international flight on CO if that makes a difference.

Thanks!