FWIW, the College Board approved use of a keyboard for my PG and dysgraphic son - but his dysgraphia isn't mild, he has a formal diagnosis of a Disorder of Written Expression, he has a long history of using a keyboard or scribe for all testing and written assignments, had years of OT for fine motor and handwriting delays, and we had a recent evaluation showing handwritten writing performance significantly behind age norms with a significant achievement improvement with the use of keyboarding.
According to their website, the ACT won't even consider letting my son use a keyboard because he can physically hold a pencil.
I'd apply for accommodations as soon as you have all the relevant documentation lined up: once you are approved, the accommodations are good on all subsequent testing for the College Board, at least according to the accommodations letter we got.
