We had the same thing happen to us with Delta for our May trip... went from 90 min to 46 min. With 3 kids I was really worried about it. I was going to just risk it, but later flights were filling up, and when I was watching what time our first plan was getting in for the month before it seemed like it landed late 75% of the time. If it had just been me or me and DH we would have risked it and took our chances. With the kids too we worried about missing the flight and not being able to get out together for some time... plus little kids really need to sit by a parent.
SO... while everyone said 46 min should be enough time, I called and they switched us to the next flight out which was a 2 hour layover. As it turned out, we were delayed a half hour getting out and then sat on the ground at ATL waiting to get to our gate... so when we got into the airport, we would have had like 5-10 min to make the flight. I was SO glad i had changed it!!!
With that saying... if we had landed on time, we would have been fine. It only took us like 20 min even with kids to get from C terminal up to A. The train system is quick. But personally I wont do less than an hour again there.