Folk from: https://gist.github.com/sdrew/5230424 with some tuning.

HH:mm formatter for UITextField in Swift

lazy var timeFormatter: NSNumberFormatter! = {
        var formatter = NSNumberFormatter()
        formatter.numberStyle = .NoStyle
        formatter.groupingSize = 2
        formatter.groupingSeparator = ":"
        formatter.usesGroupingSeparator = true
        formatter.maximumFractionDigits = 0
        formatter.minimumIntegerDigits = 4
        formatter.maximumIntegerDigits = 4
        return formatter
    }()

extension YourController: UITextFieldDelegate {
   
    func textField(textField: UITextField, shouldChangeCharactersInRange range: NSRange, replacementString string: String) -> Bool {
        var input = textField.text.stringByReplacingOccurrencesOfString(":", withString: "")
        
        if countElements(string) == 0 {
            input = input.substringToIndex(advance(input.startIndex, countElements(input) - 1))
        }
        else {
            input = input.stringByAppendingString(string)
        }
        let value = NSNumber(double: (input as NSString).doubleValue)
        textField.text = timeFormatter.stringFromNumber(value)
        
        return false
    }
    
    func textFieldDidBeginEditing(textField: UITextField) {
        if countElements(textField.text) == 0 {
            textField.text = "00:00"
        }
    }
    
    private func validateTime(time: String) -> Bool {
        if countElements(time) == 0 { return false }
        let array = time.componentsSeparatedByString(":") as [NSString]
        if let hour = array.first?.integerValue {
            if hour > 23 { return false }
        }
        
        if let minute = array.last?.integerValue {
            if minute > 59 { return false }
        }
        return true
    }
    
}