Reactivation of requested hours display for partial day requests

Is it possible to give organizations the option of choosing how it wishes its employees to request partial day requests?  At present, employees who wish to request a partial day are presented with a specific time range in the Requested Time fields (e.g., 08:00 - 10:00) as opposed to requesting a number of hours (e.g., 1 hour, 2 hours / 0.25 days).  Is it possible to deactivate the drop-down menus with specific time ranges and reactivate the option of typing in the generic number of hours requested?  Thank you.