I worked 90% 12 hour shifts while I was in graduate school - until the second year then I dropped to 75%. Still had to call in to be able to finish papers on time.
Grad school is great - but the amount of reading is pretty outrageous - I was doing 6 credits a quarter only on Fridays - that worked. While the amounts of reading is high - it is great stuff - so I would work less if I were you. Papers, projects and group stuff galore - no testing however! I was in an MN program.
I came up with my 8 Simple Rules for grad school when I was mentoring the incoming class.
1) you will not fail.
2) you will not read everything.
3) you will find a project idea.
4) you will gain confidence in yourself.
5) you will become a better writer.
6)You will learn to research.
7) you will get through the dark days.
8) You will be sad when it is over so remember to enjoy the process.
#8 it turns out is very true. I miss it
Grad school is entirely different that your BSN program. You aren't treated like an undergrad - and there are expectations that go along with that.
Treat yourself and the experience with the respect it desires - do it part time - and don't treat it as something to get past. It is a unique experience.