NEW YORK ( MainStreet) -- If you're a job applicant -- even one with multiple opportunities on the table -- the clock is always ticking on that other side of the table. There's an expiration date on any outreach from human resources personnel who call or email with either an offer for employment or an offer of a job interview. Assurance Wireless, a Warren, N.J., telecommunications provider, has the goods on the patience (and impatience) of human resources staffers when it comes to contacting job applicants. The firm released a study this week showing, among other things, that if job applicants don't respond to an HR phone call within 48 hours, the company will pull any job offer or interview offer -- and they won't be calling back. hiring manager hanging. If you get a call, whether you want the job or not, call back that business day if possible. Even if you don't want the job, HR people are a close-knit group, and you may develop a reputation in your industry as a prima donna who can't be bothered to return a phone call. Sounds simple, right? But as the Assurance study shows, it's something HR professionals take very seriously -- and so should you.