I do it pretty often. I always walk. Walk is about five to eight minutes. You can take a cab if you are running late. Won't make the cab driver happy but will cost five dollars and take two minutes. 90% of the time you can get thru security in ten minutes or less (either terminal). I usually can do gate to gate in 20 minutes or less but I know exactly where I am going - It is not well marked. The real issue is,in my experience, the Express flights are rarely on time. If you are flying mid-day you have a much better chance. If you are trying to get in after 3pm - I would check to see the average arrival time of your inbound flight