An odd struck bell is one which strikes sooner, or later, than you would expect it to. This could be at one or both strokes. An afternoon, day, weekend, period of time over which ringer's go and ring at other towers. Most commonly days, but weekends are becoming popular. There will usually be about 5 to 8 towers in a day, depending on distance, time at each tower, etc.
Most outings tend to include at least one pub.