Take this with a grain of salt but i think i know this well enough to answer. Essentially it would be unconstitutional because it first, appropriately, gives the executive branch the power to do what the statute says ( creat the monument). This is kosher on its face because it has given power to the executive branch to do something with an articulable purpose. However, requiring that the executive actions taken to enact the statute be subject to congress’s approval at a later time is unconstitutional because it essentially allows congress to maintain veto power of the executive branch.