I had the same issue last season. I was pretty new into long distance riding and I was doing it on a brand new bike. After every ride longer than 40 miles, I was getting numb pinky and ring finger. The longer the ride, the longer it took for it to recover.

When I started getting paranoid, I opted for a a bike fitting and handlebars with drops. Drops give you significant more positions for you to move your hands. The bike fitting made sure that I didn't have too muhc weight on my handle bars. I also opted to put a reminder in my bike computer that every 15 minutes, a timer goes off (just a beep), which reminds me to check my posture. I either change my hands, check my sitting on the saddle, drink water, etc. Remember the ulnar nerve starts in the neck and goes through your whole arm.... sometimes the blockage happens in the Elbow, so it is important to keep your upper body relax - shake it often and make sure that you are not holding those bars too hard.

These changes seem to solve my issue. I was able to do a century ride last year and ended without any pain or numbness on my fingers.

As far as recovery from numbness, if it takes longer than 2 weeks for your body to recover, you might need to see a doctor to help you NSAID/steroids shot directly into the blockage.

Hope this helps!