I am using the following to pause the javascript for a few seconds:
setTimeout(start_countdown(),3000);
It does not work, the function is
You need to pass a function reference. You are passing a function's return value.
The difference is this: one is a blueprint of the function you want to happen, the other means you are executing the function immediately and passing its return value to setTimeout.
setTimeout(start_countdown, 3000);
If you want to do something more complex than simply call a named function, OR you want to pass a param to the named function, you'll need to instead pass an anonymous function to the timeout and call your function within that:
setTimeout(function() {
start_countdown(/* possible params */);
/* other code here as required */
}, 3000);