If you're hired as a per diem nurse without benefits, you're not going to get benefits, no matter how many hours you work. As already noted, employers are not required by law to offer anyone
benefits; as long as they follow their own established policies and treat everyone equally/fairly in accordance with their own policies, they're not doing anything wrong. You agreed to no benefits when you took the per diem position.
"Maternity leave" varies greatly. Since v. few American employers offer paid maternity leave, how long people stay out largely depends on how long they can afford to stay home. I work per diem and recently did the same thing you're asking about, worked full-time temporarily to cover for a nurse on maternity leave (no, I didn't get benefits during that time
), and that nurse came back to work full-time after just six weeks
-- as soon as her physician cleared her physically to return to work -- because her short-term disability ended as soon as her physician said she was able to work, and her family couldn't get along without her income. Other people stay out longer periods of time, or, sometimes, never
return to work.
It is standard practice that per diem nurses get paid more (often quite a bit more) per hour than the permanent staff nurses, to compensate for the irregular schedule and lack of benefits. It's safe to assume that, if you take a permanent, regular staff position in the future, you will get paid less per hour than you're making now.
New graduates are rarely in a position to negotiate salary or anything else about a job, since new grads have little to offer employers. In fact, when the costs of hiring and orientation are taken into account, new graduates are a financial burden to employers for the first year or so. The way it usually works is that an employer offers you their standard salary/package for new graduates, and, if you
don't like it, there are plenty of other new grads who will be happy to get it (esp. these days, where there are so many new grads and so few jobs -- employers are definitely "in the driver's seat" these days), so the employer moves on to the next person on the list.