saveCase : function(component, event, helper){

    helper.validate1(component);
    helper.validate2(component);

    var isValidDate = helper.validateExtDate(component);
    //Other custom logic
    helper.createCase(compoent); //Saves case
}

validateExtDate:function(component)
{
    var caseRec = component.get("v.case");
    var action = component.get("c.getResponseDeadlineOnEdit");
    action.setParams({
                      "cs":caseRec

    });
    action.setCallback(this,function(response){
             this.processresults(response, component);
    });
    $A.enqueueAction(action);
},

processresults : function(response,component) {
    var extnsDate = component.find("respExtdate");
    var extnsDateVal = extnsDate.get("v.value");
    var extDate = new Date(extnsDateVal);
    var state = response.getState();
    if(state === "SUCCESS") {
         var deadlinedate= response.getReturnValue();
         if(extDate <=  deadlineDate) {
                    extnsDate.set("v.errors", [{message: "Please select a different date” }]);
        }
}