timeMask.js

angular.module('foobar', [])
    .directive('timeMask', function(){
        function format(input){
            var time;
            time = input.split(':');
            if(time.length){
                if(time[0] == ''){
                    time[0] = '00';
                    time[1] = '00';
                }
                else if(time[1] == ''){
                    time[1] = '00';
                }

                if(parseInt(time[0], 10) > 23){
                    time[0] = 23;
                }
                else if(parseInt(time[0], 10) < 10){
                    time[0] = '0' + parseInt(time[0], 10);
                }
                if(parseInt(time[1], 10) > 59){
                    time[1] = 59;
                }
                else if(parseInt(time[1], 10) < 10){
                    time[1] = '0' + parseInt(time[1], 10);
                }
            }

            if(time.length == 1){
                time[1] = '00';
            }
            return time.join(':');
        }
        return {
            require : 'ngModel',
            restrict : 'A',
            link : function(scope, element, attrs, ctrl){
                scope.$watch(element, function() {
                    ctrl.$setViewValue(format(element.val()));
                    ctrl.$render();
                });
                element.bind('blur', function() {
                    ctrl.$setViewValue(format(element.val()));
                    ctrl.$render();
                    scope.$apply();
                });
            }
        }
    });

view.html

<input type="text" ng-model="foo" time-mask />