Have you also tried setting the time on the system?

Yep, I did that first thing.  I did it through the Manager using the telephone.  I also connected using Cosessions, and the time is as I had set it.  But for some reason the telephones show the time as one hour ahead.

You also need to set the time on the telephone system itself. This has to be done from one of the first 2 ports on the system (usually receptionist phone is one of them).

With this phone idle, press the FNC key, then press 9, then press #. Enter the time (I believe the format is hhmmss). Then press the FNC key again. Time should populate to the other phones.

OK- that sounds like an excellent suggestion - one problem, our phones don't have a FNC key.  I assume that means Function, but all we have is Feature, Recall, Conf, Redial, Transfer, Anser and Hold.  I've tried the key sequence on the reception phone using Feature and the other keys on the phone, but tat key sequence doesn't get me into the correct menu/prompts.  I get dialtone.  Is there an alternative path to get to the prompt where I would have hit the FNC key?

Maybe the feature key has been programmed for another funtion,or the phone you were trying to program from is not the reception phone ,which the recpt. phone is programmable in some NEC systems. I can't remember but you still might have to program the system from the programming port,One NEC system I just reset uses the same sequence as above with the exception of hold as the enter Key.Not Gosple just trying to help

OK - I finally got it. Used Feature instead of FNC. The reason that it wasn't working even when I used Feature before was that I was using the reception station, but that is not the lowest extension number. When I went to the station with the lowest extension, then it worked like a charm. Thanks to you all for your help! I got confused between port and extension.

Daylight Saving on the phones is not supported until 6.00 and higher.  If you press feature 3 from any display phone it will tell you what version of software you have.  Hope this helps.