Introduction: In the 2014 Emergency Department Benchmarking Alliance Summit, for the first time, participants recommended tracking nursing and advanced practice nurse hours. Performance data from the Centers for Medicare and Medicaid Services provides an opportunity to analyze factors associated with delays in emergency care. The purpose of this study was to investigate hospital characteristics associated with time to a diagnostic evaluation in 67 Massachusetts emergency departments from 2013 to 2014. Methods: Covariates significantly correlated with time to diagnostic evaluation, and factors associated with timely care in emergency departments were included in the stepwise linear regression analysis. Differences in nurse staffing and performance measures in trauma and nontrauma emergency departments were examined with analysis of variance and t tests. Results: Two predictors explained 38% of the variance in time a diagnostic evaluation (1): nurse staffing (P <.001) and (2)trauma centers (P <. 001). In trauma centers, the time to a diagnostic evaluation significantly increased (P = .042) from 30.2 minutes when a nurse cared for fewer than 11.32 patients in 24 hours to 61.4 minutes when a nurse cared for 14.85 or more patients in 24 hours. Discussion: Efforts to improve patient flow often focus on process interventions such as improved utilization of observation beds or transfers of patients to inpatient units. In this study, time to diagnostic evaluation significantly increased when emergency nurses care for higher numbers of patients. The findings present new evidence identifying the relationship of specific nurse to patient ratios to wait time in emergency departments.