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.
There are no exceptions. Entering the Meet Eligibility: 2015 USA Swimming year round athletes registered in a Western Zone LSC who are no older than 14 years of age as of the first day of the meet (August 5, 2015) and are designated by their LSC to participate in the meet.