Hi Kalyan,
On which version are you working? Did you implement the half day leave functionality yourself? If yes and you're working with Web Dynpro ABAP version, you will probably need to look into the following class: CL_HRESS_PTARQ_LEAVREQ_GUIBBF. The leave request form is indeed a Form UIBB with this class defined as feeder class. Then, in the GET_DATA method, some fields can be hidden/displayed depending on the data.
Hope it helps,
Julien