$(document).ready(function()
    {
        $('#datetime_from').datetimepicker(
            {
                maxDate: tdatetime,
                onSelect: function(selected,evnt) {
                    updateDateTime_from(selected);
                }
            }
        ).datetimepicker("setDate", fdatetime);

        $('#datetime_to').datetimepicker(
            {
                minDate: fdatetime,
                onSelect: function(selected,evnt) {
                    updateDateTime_to(selected);
                }
            }
        ).datetimepicker("setDate", tdatetime);
});

function updateDateTime_from(value){
$("#datetime_to").datetimepicker("option", "minDate", value);
};
function updateDateTime_to(value){
$("#datetime_from").datetimepicker("option", "maxDate", value);
};