Angularjs: automatically update date diff? - angularjs

Question

I'm using angular 1.6.1 and I would like to update date diff automatically.
Here is the service that calculate date diff
angular.module("utils", [])
.service('utils', function ($location) {
this.correctDate = function(date) {
var s = date.replace('T', ' ');
return s.replace('.000Z', ' ');
}
this.dateDiff = function(date) {
var oneMinute = 60*1000;
var oneHour = 60*60*1000;
var oneDay = 24*60*60*1000;
var oneWeek = 24*60*60*1000*7;
var oneMonth = 24*60*60*1000*30;
var now = new Date();
var d = new Date(date);
var tNow = now.getTime();
var tDate = d.getTime();
if((tNow - tDate) / oneMonth >= 1){
return Math.floor((tNow - tDate) / oneMonth) + " months";
}
if((tNow - tDate) / oneDay >= 1){
return Math.floor((tNow - tDate) / oneDay) + " days";
}
if((tNow - tDate) / oneHour >= 1){
return Math.floor((tNow - tDate) / oneHour) + " hours";
}
if((tNow - tDate) / oneMinute >= 1){
return Math.floor((tNow - tDate) / oneMinute) + " minutes";
}
return "now";
}
})
Here is the view
<div class="post__date">
<time class="published">
{{dateDiff(correctDate(article.createdAt))}}
</time>
</div>
Now date diff is updated only if I make a click anywhere in app and I even don't understand why. So I have 2 questions :
1) Why does date diff is updated everytime I click anywhere in my angular app ? (Does angular trigger a full digest everytime I click anywhere in app ?)
2) How to update automatically date diff ?