At the D1 level, I am guessing at least 7.0 but there are no hard and fast rules here. You show up at a showcase and hit a bunch of them 400 ft., some coaches may look the other way on speed.
Here would be my advice to you. Sign up for a speed and strength program. Also, learn proper technique. You may be able to shave a half second or more just by learning proper technique. PG posted one of the best articles I have ever seen on the subject so without further adieu:
Do you want to run faster? by Jerry Ford