I sent 2 GW letters last week to 2 creditors that show 30 late pays. My question is what is the usual response time from the creditors and I am assume they usually just send you a letter as response?
Starting Score: 596
Search for your creditors name + GW. You'll likely find other people's experience for that particular creditor. For example, a lot of success with Chase, some with BoA, almost never with Capital One. You'll also find e-mail address, snail mail addresses, phone #'s etc. in terms of what worked for them.
My Starting Score: EQ: 691 (11/30/11) TU98: 726 (11/30/11)
Don't give up on just one btw. Sometimes it takes a few. 
July 2013 score: EQ FICO 819, TU08 778, EX "806 lender pull 07/26/2013
Goal Score: All Scores 760+, Newest goal 800+
Take the myFICO Fitness Challenge
Current scores after adding $81K in CLs and 2 new cars since July 2013
EQ:809 TU 777 EX 790 Now it's just garden time!
June 2017 update: All scores over 820, just pure gardening now.
Strangely got a response last night from the Credit Union. They said they would not make the change as they tried to reach me about the late payment. So my claim is not legitimate.