I feel the greenery of nearby parks add a touch of nature which, aside of Central Park, is hard to get in the city without a skyscraper of some sort getting into the image, so I am suggesting, with exception of the Peace fountain, places in the outer boroughs for you to choose one (they are all very far apart from each other to tackle in one morning).
In Brooklyn, consider then Grand Army Plaza – an imposing Arc de Triomphe-like monument with Prospect Park’s beautiful canopy of trees framing it right behind. You should find plenty of inspiration there.
In the Upper West Side in Manhattan there is also the giant & surreal Fountain of Peace located in the garden outside the St. John the Divine Cathedral. The menagerie of animals and other ‘characters’ will mesmerize you, specially if you visit it at dusk or dawn.
I have seen many mid-day photos of the Flushing Meadows Corona Park (in Queens), but none of it in the early morning light.
Last, in my beloved Bronx we have City Island, a quaint single-street historic seaport community. At the end of the street there are two seafood restaurants where you can get some wonderful shots of maritime scenes, including the local congregation of seagulls and the occasional swan will amuse you, at least for a short while (take the #6 train to Pelham Bay (1 hr from the city, then a 20 minutes free transfer bus to City Island).
Best of lucks!