Yep, I usually use GVP for this method. I usually let it sit for at least 20 min though.
When I first started this method a little over a year ago, I didn't notice anything different except that my hair was more moisturized. After a few months, I noticed my diffusing time went down as well.
Different people have different hair needs, so it doesn't surprise me that some people don't notice much of a difference. My hair is very porous and very coarse, so it's been a lifesaver for me