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.
A send-off interval set can be completed in any stroke, at any pace. In this workout, you establish a set time that includes both the swim portion and the rest portion as one interval. If you aim to swim 50 meters in 45 seconds followed by 15 seconds of rest, your send-off interval would be one minute.