I don't generally email. I generally call up at member services directly to tell them my request. Once the reservation is made, I also will call up the standard Disney reservation line to verify that the request I put in through member services is listed on the reservation.
The chat feature on the member site works as well. I just added to my request ant the cast member was able to confirm the original request made during the booking.
I have heard that someone supposedly goes through the request about 3 days out and starts trying to fill them. Don't know if this is completely true, but I have read it
On the Disney Resorts board I've read pretty consistently that rooms are assigned 4-5 days out. We make our requests when we book our room or when we decide what the request is, especially since DVC room requests need to be made via MS (calling, email or chat), not fax.