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.
The long course season begins in April and runs through August. Most swimmers will take time off at the end of each of these season that will range from 2 to 4 weeks. The short course pool will be either 25 yards (in US mostly) or 25 meters (US and International). The long course pool is primarily 50 meters but I've also swam in 55 yard (Titlow Park in Tacoma is an example) pools. Most meets are run in a SC (short course) pool during the SC season and most meets are run in a LC (long course) pool during the LC season. However, during the SC season you can still find LC meets such as Grand Prix and US Open meets while during the LC season teams that only have a SC pool might host a meet as well.