Formula fields with dates and half days

Formula fields with dates and half days

Hi,

I'm currently trying to create my own leave form. I know there is an existing form but it doesn't fit my needs.
For that purpose, I added two date fields, one for the first day of leave and the other for the last day.
I can easily calculate the difference between two dates, but I did not found how I could handle half days.
I currently use two dropdown menus to get the "half day" information, but I cannot use this information in a formula field.

Do you have any ideas about my problem ? Finally, I'd like to have the information like "9,5 days for this leave".

thank you