you'll want to use && to see that it is not equal to "AM" AND not equal to "PM"
if(!TimeOfDayStringQ.equals("AM") && !TimeOfDayStringQ.equals("PM")) {
System.out.println("Sorry, incorrect input.");
System.exit(1);
}
to be clear you can also do
if(!(TimeOfDayStringQ.equals("AM") || TimeOfDayStringQ.equals("PM"))){
System.out.println("Sorry, incorrect input.");
System.exit(1);
}
to have the not (one or the other) phrase in the code (remember the (silent) brackets)