I'm not sure if this is a bug or 'as designed', but when you do any
arithmetic with time objects (especially subtraction) and the seconds
go negative (before midnight), when you print out the time you either
always get 12 am or something interesting if you are printing 24-hour
time.
A simple fix in the method print24:showSeconds:on: would be to
instead of initializing the local variable h to self hours,
initialize h to self hours \\ 24.
