Buses run from select resorts to EWWS only when events are scheduled at EWWS. Be prepared to allow plenty of travel time if you are travelling from any other location.
Buses run every 30 minutes from the following resorts: Pop Century, all 3 All Star Resorts, and CBR (Custom House stop only.) The hours of operation depend upon the event schedule at EWWS.
If you're connecting from another location, your best transfer points are Pop Century or All Star Sports, depending upon where you're starting from. Buses are scheduled to leave those 2 resorts between 5 & 10 minutes after the hour & half-hour, and arrive at EWWS around 25 minutes after. Buses will often be behind schedule when traffic is heavy entering EWWS for a major event (including Braves games.)
From a theme park, board a bus to one of those resorts; allow 1 hour to reach the resort. From another resort, you'll need to travel from that resort to a theme park, and then to one of the resorts served by EWWS buses; allow 90 minutes to travel between resorts.
For Braves games, traffic into EWWS can get very heavy as game time approaches. I suggest planning your arrival 1 hour before game time, unless you're OK with possibly missing the first inning or 2.