Eddie: That's not a problem at all. You have to understand that whether you enter the values or not...
a) anytime you enter a date in Excel, it is also entering a time value.
b) anytime you enter a time in Excel, it is also entering a date value.
Because Excel, unless you tell it otherwise, gives *today's* date, you're probably entering a start time of 17:00 and an end time of 02:00, but you're not typing in the date, so it thinks it's the same date. If you're subtracting, Excel will NOT allow negative time values, so you're probably getting ###################, right?
Try fixing it by putting the correct dates into the cells too.
It's a little easier than it sounds. For instance, you can enter "5 p" to enter 5:00 pm today, or "4/8 5 p" to enter 5:00 pm yesterday. You would have to type "4/8 5:30 p" to get that time yesterday. It doesn't matter how your cells are formatted to be viewed, you can still enter your time/dates this way.