reformatTime.java

import java.util.Stack;
import java.util.stream.Collectors;
import java.util.stream.Stream;

class Scratch {

    public static void main(String[] args) {
        System.out.println(reformat("01:20")); //1t 20m
        System.out.println(reformat("01:00")); //1t
        System.out.println(reformat("00:23")); //23m
    }

    // Reformat '01:20' to '1t 20m'
    private static String reformat(final String time) {
        Stack<String> postFixes = new Stack<>();
        postFixes.push("m");
        postFixes.push("t");

        return Stream
            .of(time)
            .flatMap(s -> Stream.of(s.split(":")))
            .map(s -> String.format("%s%s", Integer.parseInt(s), postFixes.pop()))
            .filter(s -> !s.startsWith("0"))
            .collect(Collectors.joining(" "));
    }
}