Completely depends, only a specific dept can answer this question and every dept is different.
Even the aspect of voting a member in is variable. Yet, such a questions shows you are speaking in context as a volunteer.
Reality is even career depts tend to have probation periods of 12 to 18 months and some even longer. Private EMS may have no probation. Volunteers may or may not vote on members. So yeah, there is no specific answer to your question, only an individual dept can answer this.