Key point in SpeedDemon's post, every school has a slightly different timeframe. My son had some very HA D3's asking for info in June and others in July. There are even a couple that don't start until mid-August. And like SD said, the competition no joke (at least a lot of them). Even a school like Caltech is getting upper 80's kids now. There will be a ton of D3 freshman this year and next in the low 90's.
PABaseball brings up a good point, most D3's are very expensive and only offer need based aid. If the school is going to be a level up academically and you are ok with the bill then go for it.