How can I use User-defined Cell Format?

How can I use User-defined Cell Format?

Hi,

I want to sum cells that contain data of "hours".
I could not found the way to set a value of hours over 24:00.
It start again from 0:00 if it go over 24:00

With OpenOffice I've used User-defined Cell Format like this "[H]:MM;@".
How can I set same cell format with Zoho Sheet?