Default setting for hours calculations on projects and budget calculations is in full days so if a resource is working more than the Hours per day value and the project setting is in days,
the system counts it as 1 day.
If you want to use half days on projects and budget calculation, you should switch on 'Calculate Overbooked Hours' to Yes in Custom settings.
To do this, click on Setup.
Find Custom Settings under Develop option in the App Setup section.
Click on Preempt Global Settings → Manage → Global and then click on the Edit button.
Tick 'Calculate Overbooked Hours' checkbox.
Example: When the resource has 7,5 hours per day setting and entered 12 hours on his timesheet - Actuals on the project will be dispalyed as 1,6 days.