hiring HC before dead period a big deal?

[Salt]

It's a period of time when college coaches can't contact the recruits (but the recruits can contact the coaches)...

I don't know when the dead period starts and ends this year - I think it's usually a couple weeks in December, though...

what is a dead period?

actually, they can if you read the rule referenced in the OP. They are just limited in how they can contact them, but they still can, as well as contact their parents.