This is the very core of my MetricTime prank app which can be used/repurposed to convert regular time to Metric Time.

MetricTime-Core.swift

//This is the very core of my MetricTime prank app which can be used/repurposed to convert regular time to Metric Time.
//See the full app here: https://github.com/DeveloperACE/MetricTime

func convertTime(inputTime: (hour: Int, minute: Int, second: Int), toMetric:Bool = true) -> (hour: Int, minute: Int, second: Int) {
        
        var millisecondsSinceToday = 0
        var convertedTime = (hour: 0, minute: 0, second: 0)
        
        
        if toMetric {
            millisecondsSinceToday = (inputTime.hour * 3600000 /*milliseconds per hour*/) + (inputTime.minute * 60000 /* milliseconds per minute*/) + (inputTime.second * 1000 /*milliseconds per second*/)
        } else {
            millisecondsSinceToday = (inputTime.hour * 8640000 /*metric milliseconds per hour*/) + (inputTime.minute * 86400 /* metric milliseconds per minute*/) + (inputTime.second * 864 /*milliseconds per second*/)
        }
        
        
        convertedTime.hour = Int(millisecondsSinceToday / 8640000)
        millisecondsSinceToday -= (convertedTime.hour*8640000)
        
        convertedTime.minute = Int(millisecondsSinceToday / 86400)
        millisecondsSinceToday -= (convertedTime.minute*86400)
        
        convertedTime.second = Int(millisecondsSinceToday / 864)
        //screw milliseconds
        
        return convertedTime
    }