Dialog box show/hide duration setting issue

Dialog box show/hide duration setting issue

How would I specify the duration of the effect in the show and hide
lines below. The code I insert breaks the js after I set modal to
true.
    $('#dialog2').dialog({
        autoOpen: false,
        bgiframe: true,
        modal: true,
        show:'drop',
        hide:"drop",
        width: 700,
        ......................... rest of code omitted for brevity
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