Sorry Been busy with spring,, I prune most vines at the middle to end of March here in Wisconsin and wait until now or a week ago to do my Marquette, It seems to help. I believe it stuns them for a week or 2 longer and pushes bud break back. I have no real evidence on this myself except that since I have done this I have gotten a crop.
I do not have petite pearl myself yet so I can not talk about it.