revalidating a dependent field with jQuery .validate

Question

I'm using the JQuery validate plug-in to validate my form. I have 4 fields that are related: ev_start, ev_end, ev_starttime and ev_endtime. The first two are dates, are required, and ev_end must be after ev_start. The second two are times and may or may not be required, but ev_endtime must be after ev_starttime if they are entered.

If I change an incorrect ev_endtime or ev_end the field is revalidated based on its dependencies as required. But if I change an ev_start or an ev_starttime, the dependent ev_end or ev_endtime is not revalidated. How do I fix this?

My rules look like this:

    rules: {
        ev_start: { dateCan: true, required: true},
        ev_end:{ dateCan: true,
                 minDate: ":input[name='ev_start']"
        },
        ev_starttime:{
            required: 
                function(element){
                    return $("input[name='allday']:unchecked")
                },
            time: true
        },
        ev_endtime:{
            required: 
                function(element){
                    return $("input[name='allday']:unchecked")  
                },
            time: true,
            minTime: {
                depends: function(element) {
                            return $("input[name='ev_start']").valid()
                                   && $("input[name='ev_end']").valid()
                                   && $("input[name='ev_starttime']").valid()
                                   && $("input[name='ev_start']").val()==$("input[name='ev_end']").val()
                        },
                param:  ":input[name='ev_starttime']"
            }

        }
    }

dateCan is a custom rule that checks for 'YYYY-mm-dd' date format. minDate and minTime make sure that dates and times are in the correct order. All of this works.