I think you're probably out of luck. When I fly into Bogota on a separate ticket and I am connecting with American I have to wait around until they allow me to check in. I haven't flown United for a while, but back when I was a regular United flyer they were pretty strict about not letting you drop bags more than four hours before your flight. This was throughout their system - not just Bogotá.
But, it never hurts to ask once you get there.