There are many who must miss church because they have to work. Even in monasteries, some monastics have obediences which keep them busy away from church services sometimes. The key thing, I think, however, having been a student for many years myself, is to try and make some time for going to church each week--whether on Sunday or some other day for prayer, particularly in liturgy or a corporate service. As the Lord says, the Sabbath was made for man, not man for the Sabbath. After missing church for awhile and coming back, it often becomes clear to us just how much we need these services--more than sleeping or eating or anything else. That said, if you have a task you absolutely must do, there's a blessing for that. But it's up to you to discern if it is essential that you must miss church due to work, sickness, etc. If you are in need of advice, contact your priest. That is what God has put him there for, to help people. God be with you in your studies and work!