Disable default empty service provider

Hello
please before visit here
http://www.impiantisportivipescantina.com/prenotazione-campi

Is it possible to set a service provider as default?

I would remove "Seleziona Orario" like default empty selection options and I would have only 3 options in my combo service provider and set "Mattina" as default.

Is it possible?

Thanks
Claudio