At many firms, the annual year-end push to collect outstanding client bills is well underway—and this year it could be more stressful than usual.

A report released in November by Citi Private Bank’s Law Firm Group showed that firms took longer to convert entries on their time sheets into cash in the first three quarters of 2015, compared with 2014. That could be because lawyers have not yet collected on bills, or because more of the work recorded was for deals that have yet to close.