let formatter = DateFormatter()
formatter.dateFormat = "yyyy-MM-dd HH:mm XXX"

let from = zoneFormatter.date(from: "2018-03-25 00:00 +00:00")!
let to = zoneFormatter.date(from: "2018-03-26 00:00 +00:00")!

let components = Calendar.current.dateComponents([.month, .day, .hour, .minute], from: from, to: to)
// components is 1 day, 1 hour, because I am in UK and Daylight Savings started on 25 March.