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.
On Sunday, a group of brave, brazen Aussies took part in a mass-skinny dip at a Perth Beach, successfully setting a new Guinness World Record for the largest group 'nude swim'. All 790 skinny dippers had to stay in the water together for at least five minutes, with each person required to be in as deep as their waist.