"Time" problem: Need function to find time&date - ?hours

Ok .. I have a spreadsheet i got some help with a while back . . .
Trying to add some features to it and run into an issue!

Ok ... Here are the fields we are working with!

A1= 13:30:00 17/12/2008
(in other words 1:30pm on date given) - Need to know proper cell number format!!

B1= 23:00:00
(this represents 23 hours) - format for cell is [h]:mm:ss

C1= Unknown function
(This field is my problem!!)
Answer here SHOULD be "14:30:00 16/12/2008"

I need a function for C1 (using A1 and B1) that will give me the time and
date 23 hours earlier or however many hours:mins:secs is specified in B1!
Also need to know what number format to use for both A1 and C1

First ...
That doesnt tell me the cell number format to make that work!

Secondly, tried that with just time and cell format of [h]:mm:ss and all it
gave me was ######### as it cannot show negative times!

If i just put the A1 as normal formatting and that info in the cell,
answer comes back as #value because the answer is invalid!

I thank you for attempting to help but test it yourself and you'll see it doesnt work!

Hi,

What Bob has told you is correct, you just need to make the column width wider to display the result.

The format of cell A1 is a custom format hh:mm:ss dd/mm/yyyy
The format of cell B1 is hh:mm:ss
The format of cell C1 needs to be set the same as A1