Simple implementation of x.hours.ago() and others.

time-helpers.swift

enum FloatToDate {
    case Second(Double)
    case Minute(Double)
    case Hour(Double)
    case Day(Double)
    case Week(Double)
    case Month(Double)
    case Year(Double)
    
    func ago() -> NSDate {
        return NSDate().dateByAddingTimeInterval(-timeInterval())
    }
    func fromNow() -> NSDate {
        return NSDate().dateByAddingTimeInterval(timeInterval())
    }
    
    private func timeInterval() -> NSTimeInterval {
        switch self {
        case .Second(let seconds):
            return NSTimeInterval(seconds)
        case .Minute(let minutes):
            return NSTimeInterval(minutes * 60.0)
        case .Hour(let hours):
            return NSTimeInterval(hours * 3_600.0)
        case .Day(let days):
            return NSTimeInterval(days * 86_400.0)
        case .Week(let weeks):
            return NSTimeInterval(weeks * 604_800.0)
        case .Month(let months):
            return NSTimeInterval(months * 2.63e+6)
        case .Year(let years):
            return NSTimeInterval(years * 3.156e+7)
        }
    }
}

protocol Dateable {
    var seconds: FloatToDate { get }
    var minutes: FloatToDate { get }
    var hours:   FloatToDate { get }
    var days:    FloatToDate { get }
    var weeks:   FloatToDate { get }
    var months:  FloatToDate { get }
    var years:   FloatToDate { get }
}
protocol SingleDateable : Dateable {
    var second: FloatToDate { get }
    var minute: FloatToDate { get }
    var hour:   FloatToDate { get }
    var day:    FloatToDate { get }
    var week:   FloatToDate { get }
    var month:  FloatToDate { get }
    var year:   FloatToDate { get }
}

extension Int : SingleDateable {
    var seconds: FloatToDate { get { return .Second(Double(self)) } }
    var minutes: FloatToDate { get { return .Minute(Double(self)) } }
    var hours:   FloatToDate { get { return .Hour(Double(self)) } }
    var days:    FloatToDate { get { return .Day(Double(self)) } }
    var weeks:   FloatToDate { get { return .Week(Double(self)) } }
    var months:  FloatToDate { get { return .Month(Double(self)) } }
    var years:   FloatToDate { get { return .Year(Double(self)) } }
    var second: FloatToDate { get { return seconds } }
    var minute: FloatToDate { get { return minutes } }
    var hour:   FloatToDate { get { return hours } }
    var day:    FloatToDate { get { return days } }
    var week:   FloatToDate { get { return weeks } }
    var month:  FloatToDate { get { return months } }
    var year:   FloatToDate { get { return years } }
}
extension Double : SingleDateable {
    var seconds: FloatToDate { get { return .Second(self) } }
    var minutes: FloatToDate { get { return .Minute(self) } }
    var hours:   FloatToDate { get { return .Hour(self) } }
    var days:    FloatToDate { get { return .Day(self) } }
    var weeks:   FloatToDate { get { return .Week(self) } }
    var months:  FloatToDate { get { return .Month(self) } }
    var years:   FloatToDate { get { return .Year(self) } }
    var second: FloatToDate { get { return seconds } }
    var minute: FloatToDate { get { return minutes } }
    var hour:   FloatToDate { get { return hours } }
    var day:    FloatToDate { get { return days } }
    var week:   FloatToDate { get { return weeks } }
    var month:  FloatToDate { get { return months } }
    var year:   FloatToDate { get { return years } }
}

Usage

2.days.ago()      // => Aug 4, 2014, 11:05 AM
2.hours.fromNow() // => Aug 6, 2014, 1:05 PM
2.5.hours.ago()   // => Aug 6, 2014, 8:35 AM
1.year.fromNow()  // => Aug 6, 2015, 5:45 PM