While I have never traveled this route during peak travel times...I would say it would take about apx. 15/20 minutes to get to the closest express bus. Which as BKQC has stated is located at the Rivergate Shopping Center (the Steele Creek Express - 41x).
CATS Bus Schedules
Here is an article from the Lake Wylie Pilot that tells a little more about it:
Lake Wylie Pilot - Local (broken link)