Conditional Formating ctl+shift+;

[Met Fan]

I am designing time sheets for our salaried employees. I want them to populate the times in the cell using ctrl+shift+; so that it enters the system time and not what ever time they want.

Is there a conditional formatting option that would prevent them from entering the time in any other way? I do not want to use Macros since not all users have macros enabled.

Thanks