Medellín is 2 hours behind Santiago
Best overlap: 10:00 AM to 6:00 PM in Santiago is 8:00 AM to 4:00 PM in Medellín.
10:00 AM to 6:00 PM in Santiago is when Medellín is also working, at 8:00 AM to 4:00 PM their time. The 2-hour gap barely gets in the way — you've got 8 hours of overlap, so pick whatever time fits the agenda. Just remember Santiago changes its clocks for daylight saving and Medellín doesn't, so confirm the overlap whenever the seasons turn.