An offer of that size indicates that matt is regarded as a stud player. If he takes that offer for granted and lets it lay on the table for months, it can be pulled, especially if the coaches get the impression he is shopping around, may never commit, and that their next choice might get away if they don't act to put their money to work for them.
Like it or not, these things are happening earlier on in the process than before, and no one player can hold back that tide. Matt needs to deal with the reality he has in front of him. While I would be suspicious of any program that gave him an unreasonably short deadline, clearly the ball is in his court to get his homework done and to "fish or cut bait" within a reasonable time frame.
Taking the offer for granted is a great way to see it get pulled back. And if in the end this would've been Matt's first choice and/or best option, that would be a very bad thing to let happen.
I do think Matt could e-mail the coaches with the following thoughts:
1. I really appreciate your offer and the interest in me that you've shown.
2. I am very interested in your school and your program.
3. I was surprised to get such a great offer so early, and to be honest, I don't know if I was ready for it.
4. I am going to step up the pace on "doing my homework", but I feel I am going to need some more time to make sure I've made the right decision.
5. Can you let me know when you would need a decision from me? Or, if you get to a point where you will need a decision, would you please let me know?