A) Default Values only apply when no value exists in the field. When a new
record is created, Access will see that there's no value for txtEntryDate,
and will populate it with the appropriate value. Any further use of that row
will contain the value assigned when the record was created.
B) If you're using Date, that should only be an issue if someone starts
creating a record before midnight, but doesn't select a value from
cboEnteredBy until after midnight. Will that really an issue for you? (I
could see perhaps being concerned if you were using Now, rather than Date)
Incidentally, is there a reason why you're making the user select from a
combo box? You can write a function that returns the user's Windows Network
ID. (See
http://www.mvps.org/access/api/api0008.htm at "The Access Web" for
details). Unfortunately, though, you won't be able to use that function as a
Default Value. What you can do instead is put code in the form's
BeforeUpdate event to set the field.