The quiz module doesn't support delayed grading, but you can easily delay display of grades or finished quizzes. On the set editor page, there are two options, "Show Scores on Finished Assignments?" and "Show Student Work on Finished Tests?" The first governs whether students see their scores on the finished quiz assignment, the latter their work. In either case you can set the value to "after set answer date," in which case students shouldn't get that information until after the global set's answer date.
Hopefully that addresses your need.
WeBWorK Main Forum
How delay all quizzes being graded until a set time?
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