5-6 hours or more by walk
Are you doing a day-trip / picnic to the park? In that case you can spend all day here. The park looks the same no matter where you are in there, so I think, if you just want to visit the park, which is on your to-do list, you can do it in under 2-3 hours, and then you wanna move on to other attractions. If you are in a rush, give 1 day (2 max) to Midtown Manhattan and 1 day to lower Manhattan.
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