add/remove ms to current time

A method that accepts an int value (ms) and sums it to the current time; (it is possible)

I am building a timer to track the job and sometimes i forget to pause or need to add a few minutes to the timer.

example:

// current time 00:40:00

```js
timer.add(1500)
```

result: 00:42:00

```js
timer.remove(1500)
```

result: 00:40:00