Time calculation on ruby on rails and ajax

Question

Hello,

i have a form with 2 time_select fields, a customer calls and we need to select time of the support call begin and end.

I would like to know how to send the values to a function using ajax, would it be a good idea to use a observe field for each one of them?.

here is my form:

<p>
    <%= f.label :inicio %><br/>
    <%= f.time_select :inicio %>
</p>

<p>
    <%= f.label :fin %><br/>
    <%= f.time_select :fin %>
</p>

Regards.