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.

Mark