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.
Subject: RE: swimming 1/4 mile. In competitive swimming, a swimming mile is 1650 short course yards or 66 lengths. So, 400 yards or 16 lengths, would be the rough equivalent of a 1/4 mile. Also, most triathlons that use pool swims use 400m for the 1/4 mile.