Are you planning on taking Magical Express? If so, that likely means you won't make it to BLT until around 10:40. Figure 30 minutes for check in and that puts you at 11:10. Walking to Magic Kingdom is another 10 minutes so that has you there at 11:20. You are supposed to check in 15 minutes ahead of time so you have about 25 minutes to play with if your flight is delayed, ME takes longer, or there is a long line at check-in. I think you would likely make it, but I would still be a bit nervous and might see about moving it to 12:30, just to be safe.