Definitely too late to schedule a subject test for this admission cycle. The next test date available is May 5th, about one week before admission results come in. MIT says that January test dates are the last exams accepted. Besides there are no SAT reasoning tests or subject tests given in February and no subject tests given in March or April.
I would imagine that the only exceptions would be for reasons beyond a student’s control, like you were registered but your test was cancelled because of something like a hurricane, or you couldn’t make the exam date because of a documented illness.