How do I round minutes to the nearest multiple of 5?

Very few

Date

questions have an easy answer, but this is one of them. Yay!

Under the covers

Date

is just a floating point count of the number of seconds since a reference date. If you round that count to the nearest 300.0, you get a five minute boundary.

For example:

let original = Date(timeIntervalSinceReferenceDate: 532956026.349427)
print(original)     // prints: 2017-11-21 11:20:11 +0000
let rounded = Date(timeIntervalSinceReferenceDate: (original.timeIntervalSinceReferenceDate / 300.0).rounded(.toNearestOrEven) * 300.0)
print(rounded)      // prints: 2017-11-21 11:20:00 +0000

This only works because:

• All regions use the same concept of time, that is, hours, minutes and seconds. This stands in stark contrast to larger date components — like day, month and year — where different regions have very different calendars.

• Date

  ignores the concept of leap seconds.

Share and Enjoy
—
Quinn “The Eskimo!”
Apple Developer Relations, Developer Technical Support, Core OS/Hardware

let myEmail = "eskimo" + "1" + "@apple.com"