I assume the crop was planted for hay with cattle in mind, or dairy cows, due to the 20 acre size. I understand its a good mix, as timothy uses little p&k and utilizes the N from the alfalfa.

We end up with quite a bit of timothy in and around some of our plots, I think you'll find that the deer will pretty much ignore that, in favor of the alfalfa. Timothy can spread quite fast if allowed to go to seed, since each seed head produces hundreds of tiny seeds. We keep all the serious deer plots mowed to avoid reseeding of the timothy.

The alfalfa grows very somewhat slow to start, you'll likely have deer on it right after germination, but not like you'll experience net summer, once it comes on.