If there is any chance you will need accommodations for board exams, you need to get approved for them for MCAT. The time crunch of Step 1, is more challenging for many people, than the time pressure on the MCAT. When you apply for accommodations on an NBME exam, they are highly unlikely to grant it if you didn't apply for it for the mcat or other exams unless you have a glaring interval change medically documented (i.e. sustained a head injury between them)