If you need a particular day off, you should call the OE scheduling folks and request a day off. When I went through indoc, they asked us if we had any conflicts and they worked around it. They should be willing to work with you provided they haven't built a schedule for you and changing it requires significant rescheduling of others. I'd call them as soon as you can. It doesn't hurt to ask the question. Beg for forgiveness late.