A typical question in project management is. "Who owns the float?" In where legal documents do we see the real answer to this question?

i don't thing i ever seen a legal document where it refers to the ownership of the float. however, If the vendor/contractor owns the float, he may use it to absorb the delay effects of an event that does not entitle him to an extension of time under the contract.

from the employer presp. he may use it to reduce the extension of time that would otherwise be due to the contractor.

i generally  suggests that the Project owns the float, or in other words float belongs to either the contractor or the employer depending who claims it first in a factual sense.