Incrementing dates by one hour returns bad result
 

I am currently attempting to write code that will take
input from the user as to the start and stop date of an
event of interest, then generate a range of dates by hour
(e.g. 1/1/03 12:00 AM, then 1/1/03 1:00 AM, etc.) between
the specified dates. These will be used to vlookup y
values corresponding to the dates on another sheet. I am
having what seems to me to be a strange problem and did
not find any information on it in net searches or by
searching this group.

The following is the portion of the code relating to the
problem:

Storing the start date information from the user:

CommandButton1_Click_EnterEvent:
Dim StartDate As Date
StartDate = DateValue(InputBox("Enter event start
date:", "Event Start Date"))

Later in the code I use a do loop to generate the dates
and print them to a worksheet:

Dim Counter As Integer
Dim dt As Date
dt = StartDate + TimeValue("12:00 AM")
Counter = 8
ActiveSheet.Cells(Counter, 2) = dt
Do While dt < StopDate
dt = dt + TimeValue("01:00:00")
Counter = Counter + 1
ActiveSheet.Cells(Counter, 2) = dt
Loop

If I use a date increment of one minute (e.g. dt = dt +
DateAdd("n" , 1 , dt), this works. If I use an increment
of two hours or one day it works. But if I use an
increment of one hour (done as shown above, or with
DateAdd, or by simply saying "dt = dt + (1 / 24)," the
dates fill in successfully until 11:00 PM--but then the
next line is midnight the same day instead of midnight the
next day.

Example output in worksheet column:

5/1/2003, 5/1/2003 1:00, 5/1/2003 2:00, ... ,5/1/2003
23:00, 5/1/2003 0:00 (not 5/2/2003 0:00 as it should be).

If I check this by dragging the first few dates over to
the next column and autofilling them manually, the dates
proceed to 5/2/2003 0:00 as they should. Also, the
first "5/1/2003" does indeed represent 5/1/2003 0:00
because the dates are used in a lookup table--and the
first "5/1/2003" returns the same lookup value as the
second "5/1/2003 0:00."

I am at the end of my rope with this one. Thanks in
advance for your time and assistance.