For those of you asking about the ER Tech (certifications and hours) it depends what hospital you work for. I know some hospitals require their techs to be EMT-Ps (i think those are few in number though and they have more responsibility and are allowed to do more). My hospital only requires a person to pass a test through the Human Resourses/Employment office to be considered. Much of the rest is taught in orientation and on the job. If you have taken an EMT-B class, or CNA class you will pass the test. I do have coworkers that have had no clinical experience, but simply taught themselves to take blood pressures, pulse, respirations (because that's what you mainly have to do for the test, plus add, subtract and have common sense). So, basically, it depends on the hospital and you should call the employment offices and ask what the requirements are for ER Techs/ER Nursing Assistants.
As far as time committment goes, personally I can work as much as I want or as little as I want. You'll find many students in these positions, so they are very flexible. Shifts can range from 8-12 hours, though some are shorter. Many students are just fill ins when the regular 40 hour or 20 hour employees don't fill up the needs. I work about 20 hours a week, but there are other students that work with me every other week, once a week, whatever they can. Another bonus is that some hospitals (mine included) offer tuition reimbursements (not all reimbursed of course, but a substantial amount of money). Hope this helps