Anyone who's done any research quickly learns that there are some structural problems that can happen when oil paintings are varnished before the three to six month drying time.
Of course, as artists that sell work, this is somewhat problematic. We don't necessarily like storing pieces for that long. Fortunately, times change. New studies and experiments happen. While I'm not a chemist or materials expert, I am a researcher-type and I'll share some art "street talk" about it here.