InfoPath Dev

Hi I'm building a booking form in which people can choose 3 options to book something on a daily basis. The form is using 3 x Radio buttons with the choices of 9am / 12pm / 3pm. The main thing I would like to do is have a pop up message ( using a hidden field or section ) that displays a message if the user picks a time on the form that is before the actual time in the day. EG - User is filling in the form at 11.50 am but chooses the 09.00 am option and is too late for that time. The message would then state that the time has already passed etc. is there a rule that could do this or something similar. Thanks in advance.

I think you mean Option Button.. Please take a look at the attached sample.  

1. When you select an Option Button, rule checks current date-time, and get time part.
2. Then depends on the current time, and selected button, set error message if its too late.
3. If not, set the error message = "" 
4. Set format rule for the section contains Message to hide if the message is blank. 

it is very simple implementation, assuming no one book for tomorrow's reservation :-).  Though you can modify conditions as you like..

 Sorry! the previous attachment is InfoPath 2013 form. So now, attached one saved for InfoPath 2010. Hope it will work.....