Dropdown option change depends on time in AngularJs

You can take the differences in date

For example your current time in JSON is

Thu Mar 23 4:10:44 -0700 2017

Setting this as your current time

var currenttime = new Date($scope.data["time"]);

Now you can loop through each property in your object and compare start time and end time with current time

for (var key in $scope.data) {
        if (key !== "time") {
        var starttime = new Date($scope.data[key]["start_time"]);
        var endtime = new Date($scope.data[key]["end_time"]);
        var startdiff = (currenttime - starttime);
        var enddiff = (currenttime - endtime);
            if(startdiff < 0 && enddiff < 0){

          $scope.text = ("Next activity \""+key+"\" in "+Math.abs(Math.round(((startdiff % 86400000) % 3600000) / 60000))+"min");
          $scope.activity="Next";
          break;
        }
        else if(startdiff > 0 && enddiff > 0)
        {
            //Activity has finished
        }
        else{
            $scope.text = ("On going "+key);
          $scope.activity = key;
          break;
        }
        }
        } 

if startdiff > 0 && enddiff > 0 condition is true --> Activity has finished

if startdiff < 0 && enddiff < 0 condition is true --> You are between previous and next activity

else --> You have an on going activity

The line

Math.round(((startdiff % 86400000) % 3600000) / 60000)

will give you difference in minutes

As this will always be a -ve value surround it in Math.abs(...)

Here is the FULL EXAMPLE