@wrosie I'm not sure whether this might help you, but you can indirectly check on the "status" of your MAO by clicking on the job listing/post on the job board. If they've rejected your MAO, it should say something like "this make an offer has been declined" in red font near the top of the job description page. If they haven't made a decision or are still "processing/considering" your MAO, it will say something like "you have already submitted an offer for this job" in red font near the top of the page. I'm not sure how to cancel a MAO without declining the shop itself, but this way you can check if they've already declined your MAO (since they don't email about rejecting a MAO) or if they might still be considering it.
My MAOs are usually accepted or declined within a few hours. Sometimes if I MAO in the evening, they won't accept/reject it until sometime the next day, but I don't think it's ever taken more than 24 hours for a decision.
Sorry if that doesn't help much!