Calculate time

How fast can you calculate the total time if i say 4Hrs 33min + 8 hours 58 min? Here is an easy method(thanks to my sis for sending the same) by a small girl

http://www.ezmathtrix.com/siri.php

Here is the content

This Time Constant provides a simpler way of calculating time units compared to conventional ways that involve additional steps. Time units of hours/minutes in the following example can be substituted with minutes/seconds Suppose A = 3 hours / 40minutes and B = 1 hour / 50minutes Example:
Apply Siri Time Constant, only if the minutes in A & B equal or exceed 60. Then first convert these numbers into simple numbers like 340 and 150
By Adding A and B (340 + 150), this would equal to 490 + Siri Time Constant (40) = 530 (5 hours/30minutes)
By Subtracting B from A (340 - 150), this would equal to 190 - Siri Time Constant (40) = 150 (1 hour/50minutes) Simple Formula using Siri Time Constant: A +/- B = C +/- Time Constant (40)
(A = hr/min and B = hr/min just like in above example)
Addition: A + B = C + Time Constant (40)Subtraction: A - B = C - Time Constant (40)