From the ever dependable Fr. Z at http://wdtprs.com/blog/ :-
"From a reader…
I work 12 hour shifts at a hospital, including 1 weekend a month. This means even Saturday night Mass is out of the question. Is it a sin to miss Mass because I am required to work?
I will assume that there are no more Masses available after your shift within a reasonable distance. If that assumption is correction, NO, you do not sin by missing Mass in those circumstances.
People are not held to the impossible. If for the sake of your vocations that job is critically necessary, and therefore you have no flexibility on Sundays, then you are stuck.
However, in many places there are “last chance” Masses. You want to be sure about your options. Do some research.