I don't have Raynauds Syndrome but I Can explain about the 20 mins delay. I noticed this past winter when I rode that about 30-45 mins after I got to work - I got Really cold all over - as in chilly, shivering cold. I would drink some hot tea and be fine. Then it would happen again when I got home. I finally figured out it was my core cooling down which for whatever reason took that long to cool. It always seems to take my hands and feet longer to warm up once the cool-down happens but I keep fingerless gloves here at work and have a footrest heater so that was a big help. I'm guessing it's taking about 20 mins for your body to stop pumping blood to the extremeties to keep them warm so that's why you're noticing the coldness and whiteness then instead of during your ride. As for keeping what warm - you lose a Lot of heat from the top of your head and your extremeties is the First place your body will pull warmth. So cover your head and your fingers and toes. Hmmm......just occurred to me, if I kept a hat on when I was done riding, I might not cool down so fast!!!!.....thoughts for next winter!
Life should NOT be a journey to the grave with the intention of arriving safely in an attractive and well preserved body, but rather to skid in sideways, champagne in one hand, strawberries in the other, body thoroughly used up, totally worn out and screaming: "Yeah Baby! What a Ride!"