Another, possibly better option, is to parse the date as you recieve the JSON.
I use the following function:
(function() {
    if (JSON && !JSON.parseWithDate) {
        JSON.parseWithoutDate = JSON.parse; //Store the original JSON.parse function
        var reISO = /^(\d{4})-(\d{2})-(\d{2})T(\d{2}):(\d{2}):(\d{2}(?:\.\d*)?)Z$/;  
        var reMsAjax = /^\/Date\((d|-|.*)\)[\/|\\]$/;  
        JSON.parseWithDate = function (json) {  
            /// <summary>  
            /// parses a JSON string and turns ISO or MSAJAX date strings  
            /// into native JS date objects  
            /// </summary>      
            /// <param name="json" type="var">json with dates to parse</param>          
            /// </param>  
            /// <returns type="value, array or object" />  
            try {  
                var res = JSON.parseWithoutDate(json,
                function (key, value) {  
                    if (typeof value === 'string') {  
                        var a = reISO.exec(value);  
                        if (a)  
                            return new Date(Date.UTC(+a[1], +a[2] - 1,   
                                                     +a[3], +a[4], +a[5], +a[6]));  
                        a = reMsAjax.exec(value);  
                        if (a) {  
                            var b = a[1].split(/[-+,.]/);  
                            return new Date(b[0] ? +b[0] : 0 - +b[1]);  
                        }  
                    }  
                    return value;  
                });  
                return res;  
            } catch (e) {  
                // orignal error thrown has no error message so rethrow with message  
                throw new Error("JSON content could not be parsed");  
                return null;  
            }  
        };  
        JSON.dateStringToDate = function (dtString) {  
            /// <summary>  
            /// Converts a JSON ISO or MSAJAX string into a date object  
            /// </summary>      
            /// <param name="" type="var">Date String</param>  
            /// <returns type="date or null if invalid" />   
            var a = reISO.exec(dtString);  
            if (a)  
                return new Date(Date.UTC(+a[1], +a[2] - 1, +a[3],   
                                         +a[4], +a[5], +a[6]));  
            a = reMsAjax.exec(dtString);  
            if (a) {  
                var b = a[1].split(/[-,.]/);  
                return new Date(+b[0]);  
            }  
            return null;  
        };  
        JSON.stringifyWcf = function (json) {  
            /// <summary>  
            /// Wcf specific stringify that encodes dates in the  
            /// a WCF compatible format ("/Date(9991231231)/")  
            /// Note: this format works ONLY with WCF.   
            ///       ASMX can use ISO dates as of .NET 3.5 SP1  
            /// </summary>  
            /// <param name="key" type="var">property name</param>  
            /// <param name="value" type="var">value of the property</param>           
            return JSON.stringify(json, function (key, value) {  
                if (typeof value == "string") {  
                    var a = reISO.exec(value);  
                    if (a) {  
                        var val = '/Date(' +   
                                  new Date(Date.UTC(+a[1], +a[2] - 1,   
                                           +a[3], +a[4],   
                                           +a[5], +a[6])).getTime() + ')/';  
                        this[key] = val;  
                        return val;  
                    }  
                }  
                return value;  
            })  
        };  
        //Make Date parsing the default
        JSON.parse = JSON.parseWithDate;
    }
})();
Which is taken from here: http://codepaste.net/i89xhc, except that I overwrite the standard JSON.parse function with this version that parses the date. This means that Angular will parse ASMX dates automatically from all JSON it sees.
You could also write a custom transform using angular $http transformations. See: https://docs.angularjs.org/api/ng/service/$http