This means that the battery is discharged down to 10.5 volts over a 20 hour period while the total actual amp-hours that it supplies are measured. Sometimes ratings at the 6 hour rate and 100 hour rate are also given for comparison and for different applications.
Pool meets are usually no more than 4 hours, but beach meets last about 7 hours. It depends how many events are in the meet. And then if it is a really big meet (like a tournament kind of) it can last days. Hope that helps.
1 Those bursts of speed may last 30 seconds to a minute. After each interval, slow down and let your heart rate come back down.  Swimming: Swim a length, rest for 30 seconds, swim another length, and repeat until you've swum six lengths, suggests Guy Edson, technical director of the American Swimming Coaches Association.