You can add hours, minutes, seconds and nanoseconds:

LocalTime time = LocalTime.now();
LocalTime addHours = time.plusHours(5); // Add 5 hours
LocaLTime addMinutes = time.plusMinutes(15) // Add 15 minutes
LocalTime addSeconds = time.plusSeconds(30) // Add 30 seconds
LocalTime addNanoseconds = time.plusNanos(150_000_000) // Add 150.000.000ns (150ms)

import java.time.LocalTime;
import java.time.ZoneId;
import java.time.temporal.ChronoUnit;

public class Test {
    public static void main(String[] args)
    {
            ZoneId zone1 = ZoneId.of("Europe/Berlin");
            ZoneId zone2 = ZoneId.of("Brazil/East");

            LocalTime now = LocalTime.now();
            LocalTime now1 = LocalTime.now(zone1);
            LocalTime now2 = LocalTime.now(zone2);
            
            System.out.println("Current Time : " + now);
            System.out.println("Berlin Time : " + now1);
            System.out.println("Brazil Time : " + now2);
            
            long minutesBetween = ChronoUnit.MINUTES.between(now2, now1);
            System.out.println("Minutes Between Berlin and Brazil : " + minutesBetween +"mins");          
    }
}

There are two equivalent ways to calculate the amount of time unit between two LocalTime: (1) through until(Temporal, TemporalUnit) method and through (2) TemporalUnit.between(Temporal, Temporal).

import java.time.LocalTime;
import java.time.temporal.ChronoUnit;

public class AmountOfTime {

    public static void main(String[] args) {

        LocalTime start = LocalTime.of(1, 0, 0); // hour, minute, second
        LocalTime end = LocalTime.of(2, 10, 20); // hour, minute, second
        
        long halfDays1 = start.until(end, ChronoUnit.HALF_DAYS); // 0
        long halfDays2 = ChronoUnit.HALF_DAYS.between(start, end); // 0
        
        long hours1 = start.until(end, ChronoUnit.HOURS); // 1
        long hours2 = ChronoUnit.HOURS.between(start, end); // 1
        
        long minutes1 = start.until(end, ChronoUnit.MINUTES); // 70
        long minutes2 = ChronoUnit.MINUTES.between(start, end); // 70
        
        long seconds1 = start.until(end, ChronoUnit.SECONDS); // 4220
        long seconds2 = ChronoUnit.SECONDS.between(start, end); // 4220
        
        long millisecs1 = start.until(end, ChronoUnit.MILLIS); // 4220000
        long millisecs2 = ChronoUnit.MILLIS.between(start, end); // 4220000

        long microsecs1 = start.until(end, ChronoUnit.MICROS); // 4220000000
        long microsecs2 = ChronoUnit.MICROS.between(start, end); // 4220000000

        long nanosecs1 = start.until(end, ChronoUnit.NANOS); // 4220000000000
        long nanosecs2 = ChronoUnit.NANOS.between(start, end); // 4220000000000
        
        // Using others ChronoUnit will be thrown UnsupportedTemporalTypeException.
        // The following methods are examples thereof.
        long days1 = start.until(end, ChronoUnit.DAYS); 
        long days2 = ChronoUnit.DAYS.between(start, end); 
    }
}

LocalTime is an immutable class and thread-safe, used to represent time, often viewed as hour-min-sec. Time is represented to nanosecond precision. For example, the value "13:45.30.123456789" can be stored in a LocalTime.

This class does not store or represent a date or time-zone. Instead, it is a description of the local time as seen on a wall clock. It cannot represent an instant on the time-line without additional information such as an offset or time-zone. This is a value based class, equals method should be used for comparisons.

Fields

MAX - The maximum supported LocalTime, '23:59:59.999999999'. MIDNIGHT, MIN, NOON

Important Static Methods

now(), now(Clock clock), now(ZoneId zone), parse(CharSequence text)

Important Instance Methods

isAfter(LocalTime other), isBefore(LocalTime other), minus(TemporalAmount amountToSubtract), minus(long amountToSubtract, TemporalUnit unit), plus(TemporalAmount amountToAdd), plus(long amountToAdd, TemporalUnit unit)

ZoneId zone = ZoneId.of("Asia/Kolkata");
LocalTime now = LocalTime.now();
LocalTime now1 = LocalTime.now(zone);
LocalTime then = LocalTime.parse("04:16:40");

Difference in time can be calculated in any of following ways

long timeDiff = Duration.between(now, now1).toMinutes();
long timeDiff1 = java.time.temporal.ChronoUnit.MINUTES.between(now2, now1);

You can also add/subtract hours, minutes or seconds from any object of LocalTime.

minusHours(long hoursToSubtract), minusMinutes(long hoursToMinutes), minusNanos(long nanosToSubtract), minusSeconds(long secondsToSubtract), plusHours(long hoursToSubtract), plusMinutes(long hoursToMinutes), plusNanos(long nanosToSubtract), plusSeconds(long secondsToSubtract)

now.plusHours(1L);
now1.minusMinutes(20L);