in the above code, Start Timer, we are including peranthasis in the function call, but in the above function call, setInterval(increment_counter, 1000); you are not including peranthasis like increment_counter(). I tried running the code by including peranthasis in the code but the timer is not automated. the timer is incrementing after every click.
setInterval(increment_counter, 1000);
With the () you are invoking the function immediately. Above is passing the function as a reference and it will be called after the delay time.
setTimeout(“numCount()”,1000);
Using string argument… the string will be evaluated as script at end of timer delay