defcustom type

[Olivier Sirven]

Hello,

I would like to declare a defcustom variable to store a time using HH:MM
format. At first, I declared a list of integers but I would like to make
sure one using customize can't choose an invalid time representation like 25:70

I read customize elisp doc but it seems I can't find any answer in order
to do it easily without having to declare all available hours and
minutes.

What would be the best way to do it?

Thanks

Olivier