There was a typo. Try

=A1 + TIME(0, 15, 0)

which is equivalent to

=A1 + 1/(24*4)

or

=A1 + 1/96

with the cell(s) formatted as times.

In article <Ntisch.1w3oad_1127963132.7635@excelforum-nospam.com>,
Ntisch <Ntisch.1w3oad_1127963132.7635@excelforum-nospam.com> wrote:

> I am getting an error when I enter your formula as;
>
> = A1+Time(),15,0)
>
> Is there something I have left out?