I have two days where my exams are scheduled at the same time. I was told that I would be taking them the same day just one in the morning and one in the afternoon. Your IB coordinater will take care of you, it's not like they're just gonna say tough luck kid you won't be able to do the IB diploma because of your testing schedule. Don't worry about it. My more coordinate said that they will also treat us super well if we have two IB tests on the same day, hopefully, this means I get my coordinators famous brownies!