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.
USA Swimming maintains records for 25 yard, 25 meter and 50 meter pools. Participants compete in different age groups and meets depending on their achievement level and how old they are on the first day of the meet. Traditionally recognized age groups are 10 and under, 11-12, 13-14, 15-16, 17-18.