Batch editing the nth frame delay of gifs

Kind of dirty, but you can give this a try: 

// select frame and set to certain duration;
// 2023, use it at your own risk;
if (app.documents.length > 0) {
    var myDocument = app.activeDocument;
    var theCheck = true;
    var theFrame = 1;
    while (theCheck == true) {
    var theCheck = setFrameDuration (theFrame, 0.5);
    theFrame++;
    var theCheck = setFrameDuration (theFrame, 0.5);
    theFrame++;
    var theCheck = setFrameDuration (theFrame, 0.05);
    theFrame++;
    }
};
////// set delay of frame //////
function setFrameDuration (theFrame, theDelay) {
try {
var idanimationFrameClass = stringIDToTypeID( "animationFrameClass" );
// select frame
    var desc2 = new ActionDescriptor();
        var ref1 = new ActionReference();
        ref1.putIndex( idanimationFrameClass, theFrame );
    desc2.putReference( charIDToTypeID( "null" ), ref1 );
executeAction( charIDToTypeID( "slct" ), desc2, DialogModes.NO );
// set frame’s duration;
    var desc3 = new ActionDescriptor();
        var ref2 = new ActionReference();
        ref2.putEnumerated( idanimationFrameClass, charIDToTypeID( "Ordn" ), charIDToTypeID( "Trgt" ) );
    desc3.putReference(  charIDToTypeID( "null" ), ref2 );
        var desc4 = new ActionDescriptor();
        desc4.putDouble( stringIDToTypeID( "animationFrameDelay" ), theDelay );
    desc3.putObject( charIDToTypeID( "T   " ), idanimationFrameClass, desc4 );
executeAction( charIDToTypeID( "setd" ), desc3, DialogModes.NO );
return true
} catch (e) {return false};
};
////// by michael l hale //////
function GetFrameCount(){
    var ref = new ActionReference();
     ref.putProperty( charIDToTypeID( 'Prpr' ), stringIDToTypeID( "frameCount" ) );
     ref.putClass( stringIDToTypeID( "timeline" ) );
     var desc = new ActionDescriptor();
     desc.putReference( charIDToTypeID( 'null' ), ref );
     var resultDesc = executeAction( charIDToTypeID( 'getd' ), desc, DialogModes.NO );
     
     return resultDesc.getInteger( stringIDToTypeID( "frameCount" ) );
};