The argument to HttpRequest.setTimout is a millisecond value so for 2 minutes:
req.setTimeout(2 * 60 * 1000);
PS With the clarification that the desire is to make the web service call after a 2 minute delay I suggest you experiment with this Need System.schedule cron string for run once approach. In your case you would build the cron string to be 2 minutes from the current date/time.
