date(byAdding:value:to:options:) Method Behaves Strangely

Let’s try calculating one day after "2023/11/04 12:00 New York time".

let timeZone = TimeZone(identifier: "America/New_York")!
var calendar = Calendar(identifier: .gregorian)
calendar.timeZone = timeZone
 
var dateFormatter = DateFormatter()
dateFormatter.timeZone = timeZone
dateFormatter.locale = .init(identifier: "ja_JP")
dateFormatter.dateStyle = .short
dateFormatter.timeStyle = .short
 
var dateComponents = DateComponents()
dateComponents.year = 2023
dateComponents.month = 11
dateComponents.day = 4
dateComponents.hour = 12
 
// At New York 2023/11/04 12:00
let date1 = calendar.date(from: dateComponents)!
print(dateFormatter.string(from: date1))
 
// Add 1 day
let date2 = calendar.date(byAdding: .day, value: 1, to: date1)!
print(dateFormatter.string(from: date2))```

The output is:

2023/11/04 12:00  
2023/11/05 12:00  

Now, let’s try the following—also to get the time one day later:

let date2 = calendar.date(byAdding: .minute, value: 24 * 60, to: date1)!
print(dateFormatter.string(from: date2))

This outputs:

2023/11/04 12:00  
2023/11/05 11:00  

What's Causing This Difference?

It’s likely due to Daylight Saving Time (DST). But why do we get different results between the first and second examples?