Another version that works with a helper cell (like Jason's):

=--TEXT(--A1,"00\:00\:00")
(with A1 formatted as text, entering all 6 digits)
(still format it as time.)

Gomer wrote:

I'm trying to reduce the amount of keystrokes a customer needs to enter time
data. Essentially, they want to type only the numbers of an entry of
hh:mm:ss. When using a format built into Excel (non-custom), the system
turns the data into DD/MM/YY hh:mm:ss, coming up with an incorrect hour ,
minute, second conversion. any ideas?

--

Dave Peterson