swift3 – 如何将Date转换为TimeInterval,以便我可以使用if语句

if let date = messages?.date{
            let dateFormatter = DateFormatter()
            dateFormatter.dateFormat = "h:mm a"

            //let elapseTimeInSeconds = NSDate.timeIntervalSince(date)
            let elapseTimeInSeconds = Date(timeIntervalSinceNow: (date as? Date))

            let secondsInDays: TimeInterval = 60 * 60 * 24

            if elapseTimeInSeconds > secondsInDays {

                dateFormatter.dateFormat = "EEE"
            } else if elapseTimeInSeconds > 7 * secondsInDays {

                dateFormatter.dateFormat = "MM/dd/yy"
            }

            timeLabel.text = dateFormatter.string(from: date as Date)
        }

这是错误：

Cannot convert value of type ‘Date?’ to expected argument type
‘TimeInterval’ (aka ‘Double’)

错误在这一行：

let elapseTimeInSeconds = Date(timeIntervalSinceNow: (date as? Date))

我已经尝试过我所知道的并且没有任何效果.请帮忙.