In the absence type configuration, you can set up the minimum leave duration. Please go to Configuration -> Absence Types → Select your absence type → Edit
Open the Requesting tab and select the desired absence period. Values allowed here are different from days based and hours based absence types ("Duration unit" configurable while creating a new absence type). Afterwards, don't forget to click the Save button :).
3. Now, you can go to the 'Apply' tab and select a particular day. At the right side of the screen you should be able to choose the specific hours or half day absence.
Note:
Remember that this configuration is applicable only to the selected absence type. You have to repeat the above steps for each absence type with that kind of policy.