TalkPHP - Calculate

I have a script, actually in Java, but nevermind that. And it's supposed to let the user print in starttime in hours, minutes and seconds. And then the endtime in hours, minutes and seconds.

Then it calculates how many hours, minutes, and seconds it took.
Obviously it's a bit trickier than just endseconds - startseconds etc, since the startseconds could be more than the endseconds, which would result in that it took 1 more minute.

I think I recall that I had to use "%" but not sure how.
Please help. If it's to any help, here's the javacode if someone knows java, but it's really just the math calculation I need help with.

java Code:

import java.util.*;

public class Calculate
{
    public static void main(String[] args)
    {
        
        // Deklarera variabler
        String start, end, nextStart, nextEnd;
        int start_hours, start_minutes, start_seconds, end_hours, end_minutes, end_seconds, result_hours, result_minutes, result_seconds;
        
        // Initialisera den importerade klassen
        Scanner keyboard = new Scanner(System.in);
        
        // Start
        System.out.print("Starttid (tt:mm:ss): ");
        start = keyboard.next();
        
        // Mål
        System.out.print("Målgång (tt:mm:ss): ");
        end = keyboard.next();
        
        // Rensa
        keyboard.nextLine();
        
        StringTokenizer startTime = new StringTokenizer(start, ":");
        StringTokenizer endTime = new StringTokenizer(end, ":");
        
        nextStart = startTime.nextToken();
        start_hours = Integer.parseInt(nextStart);
        nextStart = startTime.nextToken();
        start_minutes = Integer.parseInt(nextStart);
        nextStart = startTime.nextToken();
        start_seconds = Integer.parseInt(nextStart);
        
        nextEnd = endTime.nextToken();
        end_hours = Integer.parseInt(nextEnd);
        nextEnd = endTime.nextToken();
        end_minutes = Integer.parseInt(nextEnd);
        nextEnd = endTime.nextToken();
        end_seconds = Integer.parseInt(nextEnd);
        
        System.out.println("\nStarttid:\nTimme: " + start_hours + "\nMinut: " + start_minutes + "\nSekund: " + start_seconds);
        System.out.println("\nMålgångstid:\nTimme: " + end_hours + "\nMinut: " + end_minutes + "\nSekund: " + end_seconds);
        System.out.println("\nResultat: Blaa");
        
    }
}