The review of research protocols by Research Ethics Committees (RECs), essential to ensure the protection of participants, has been managed in the City of Buenos Aires through the PRIISA.BA electronic platform since January 2020. The aim of the present study was to describe ethical review times, their temporal evolution, and predictors of their duration. We conducted an observational study that included all the protocols reviewed between January 2020 and September 2021. Times to approval and to first observation were calculated. Temporal trends in times, and the multivariate association between these and protocol and IRB characteristics were evaluated. 2,781 protocols reviewed in 62 RECs were included. The median time to approval was 29.11 (RIQ 11.29 to 63.35) days, and time to first observation was 8.92 (RIQ 2.05 to 18.18) days. The times were significantly reduced throughout the study period. We detected as variables independently associated with shorter time to approval to be a COVID proposal, having funding and the number of centers to perform the study and having been reviewed by an RECs with more than 10 members. Making observations to the protocol was associated with more time. The results of the present work suggest that ethical review times were reduced during study period. In addition, variables associated with time were identified that could be the object of interventions to improve the process.