Time-to-fill is a closely watched ratio for contingent workforce managers. A Staffing Industry Analysts buyer survey found it among the most cited methods used to evaluate managed service providers. And as the economy improves and the war for talent intensifies, time to fill rates could get longer.

One statistic: A CareerBuilder survey released this month of 2,192 hiring manager and HR professionals found 46% plan to increase temporary and contract hiring in 2015, up from 42% in a similar survey last year.

“Logically you would expect as the labor market tightens that fill rates will go down and time to fill will increase,” said Jon Osborne, VP of strategic research at Staffing Industry Analysts. “If it’s been tight already, now the market it is being squeezed further.”

But how quickly contingent workforce buyers can bring on those temporary workers when needed must be watched.

Time to fill “is extremely important as a service quality factor,” said Stephen Clancy, director of contingent workforce strategies, knowledge and research, at Staffing Industry Analysts. “It’s because contingent workforce buyers have a project that needs to be done in the near term, and waiting for that talent over a long period of time just is incongruent with why they are thinking of contingent work in the first place.”

Research released this week by jobs website Indeed found it is taking slightly longer to fill jobs in the US, and positions still empty after 30 days can take months to fill.

Indeed found the percentage of jobs unfilled after 30 days rose to 57.0% in the three months ended October 2014 — up from 56.2% in the same period in 2013.

Paul D’Arcy, senior VP at Indeed, said the strengthening US labor market is behind the increase. As more employers compete for workers with the top skills, it becomes harder and takes longer to fill jobs.

“IT, software engineering and healthcare are kind of the key areas where there is a tremendous skills shortage nationally,” D’Arcy said.

In the meantime, what contingent workforce managers can do is to track the metric and meet with their suppliers to stay on top of it. Improving time to fill may also require augmenting the number and type of suppliers.

However, it is difficult to place total responsibility for time to fill on staffing suppliers alone, Clancy said. This metric can be affected by other process components — including hiring/engagement managers who may take too long to make decisions or do not communicate timely feedback on potential “perishable” candidate submittals.

A solution is to “monitor the entire process and make each party in that process responsible for their contributions to produce a quality service result,” Clancy said.

Another key finding by Indeed: 30 days proved a tipping point. Positions not filled within that time frame have a 57% chance of remaining open for three months or more. While employers may still be confident after 30 days, the research shows they should look at their strategy or the time to fill could last months more.

Indeed’s report looked at all types of jobs, not just temporary agency positions. A survey of staffing firms last year by Staffing Industry Analysts found median time to fill for temporary staffing positions was five days. The time-to-fill varied by segment with median time to fill at industrial staffing firms being two days and median time to fill for IT staffing firms being 10 days.