Before starting nursing school, I was working 30-ish hours a week as a waitress, and saved as much money as I could. I got a job as a PCT in the hospital about a year ago. At the college I attend, we don't get to choose our schedule, it has already been pre-determined. Last semester I had class or clinical Monday-Friday. What I normally did was work 2 weekend shifts a month. One weekend off, and either a Saturday or Sunday of the next weekend. Definitely not enough to pay any bills other than water haha. But I work 12 hour shifts so I'm not sure what a "double" entails but I obviously can barely accomplish anything before/after one of those shifts. There were a few weekends I worked Saturday and Sunday, and I didn't get to study and was pretty tired for school on Monday.
My advice is to bust your butt and make as much money before the semester begins. You'll know when/if you get too exhausted. And I would also say that instead of volunteering at a hospital, try to get a job! That way you'll get experience and get paid.
Look at your hour:earnings ratio. Find what job opportunities you can make the most money in the least amount of time and figure out a way to tailor to your schedule so you're not spending too many hours NOT making money, but also not too many hours on the job. Nursing school has really taught me how to plan my time hour by hour lol.