Maternity leave questions...

So I gave paperwork to my ob's office who send off to a third party, paid for third party to fill it out. And I'm due march 31, I believe paperwork's said something that it needed to be filed 15 days prior to medical leave. Not sure though... Anyways my question is I'm wanting to make my last day be March 18th. That would mean ten more days of work for me since my job has gotten super stressful since we're so understaffed and making me miss my breaks and meals because I'm left alone to close my department. Also I don't really plan to return to this job after having baby, would rather find something else..It's more of a back up plan than anything. Is that plenty of a heads up to give them you think? I don't work again til Friday so thats when I would tell them.