"He drinks coffee at 6:15 in the morning."
早 by itself as an adjective means 'early'; as a noun means 'morning'
早上 is a noun meaning 'morning'
上 means, among other things, 'up' and 'previous'; 午 is 'noon'; 上午 means 'before noon'
Commonly, 早上 would be used for times earlier in the morning than 上午, which would be used for times closer to noon (like after 10am).