What are the busiest times in emergency rooms?

Depends...: Depends on your location... But usually friday and mondays are busy in the er.

Depends almost: entirely on the location of the emergency department. Busy metropolitan areas have fairly steady censuses throughout the day and evening. Suburban and rural emergency departments will slow to a degree during working hours of the weekdays and pick up in the evenings and weekends. You are kind of rolling the dice but if you truly have an emergency you will be triaged ahead of the crowd.