It can take anywhere from 18-30 minutes. Depending on how old you are, how conditioned you are, your stature, etc.
well it took me an hour
It would take a lot shorter. Fins help you swim much faster. Therefor, you will finish in a shorter amount of time.
A lap is technically 2 lengths. And every 2 lengths in 50 yards. Therefore, you would have to swim 10 lengths (or 5 laps) to complete 250 yards.
1670 yards. It is generally accepted in swimming as 1650.
It takes 8 minutes for the sunlight from the sun to get to Earth.