The ER uses a triage system. The wait time is based on how busy they are and how urgent your emergency is compared to the others already there. Once in the ER, after the patient is stabilized, he\she is either discharged or admitted. If admitted, they have to find a bed for the patient. This can result in additional waiting.
Depending on what part of the hospital you're at. I was in the labor and delivery section a few times, the longest I've been in the triage room was about an hour or So before I was admitted into a labor room, happened 3 times before I actually gave birth
Thanks! Your answer is awaiting moderation.