I took a look at this but it seems you can't do this easily but got this from here - click here
You can set the reminder default for timed appointments in Tools, Options. All day events will always default to 18 hours - this cannot be changed.
Free/Busy does not have an option to set the default status. However, appointments are always Busy and all day events are always free. If you open the new appointment form using the New button or by clicking on a time period in the day or week view Busy will be preselected. It you click on a date in the month grid, you're creating all day events by default, which are always Free.