Adding current date when choose specific option of Radio button.

Adding current date when choose specific option of Radio button.

I have a form for a Dog day care that i work for. The form has a look up tab for a dogs name and a radio button with two options "Check in" and "check Out". I would like for each time i select "Check in" the current date and time is added to the Date_time field before loading the form and adding it to the report

. I have been messing with the script and i cant get it down. I know it is fairly simple but the grammer of the script is not very easy to understand or set-up.